Inside Coverings of Walls.

Plaster is made of lime mortar, or cement mortar; the former is generally preferred for domestic dwellings because it remains porous and moisture does not condense on it.

In houses built by speculative builders, the plaster commonly used consists of a mixture of lime with road scrapings. The result is a composition which unless supported by the wall-papering, is soon damaged.

Ordinary plaster consists usually of three layers. The first is laid on with a mixture of about equal parts of lime and sand with long ox-hairs if required for ceilings. The second coat consists of slaked lime, mixed to the consistency of cream. The last or setting coat consists of a thin layer of slaked lime called plasterers’ putty. Some plaster of Paris (gypsum) may be added, to ensure rapid setting, but it should only be used in small quantities. For the internal plastering of rooms serapite (a form of cement) is now commonly employed. This is not so absorbent as mortar, but is sufficiently so to prevent condensation of moisture on the walls. Its chief advantage over plaster is that it hardens quicker and is smoother, and can be used in a single thin layer. This, however, diminishes the impermeability of ceilings for sound.

Keene’s cement and Parian cement are mixtures of calcined gypsum and other substances; Keene’s cement being the hardest, and capable of receiving a high polish.

Selenitic cement contains a small proportion of plaster of Paris ground along with lime. Lime may also be selenised by the addition of any other sulphate, or of sulphuric acid. The presence of the sulphate causes the lime to set rapidly. Selenitic cement is useful in plastering, as a backing of cements, such as Parian.

The treatment of the internal wall-surface of a room differs according to circumstances. Lime-washing is suitable only for stables and other outbuildings. It is made by the addition of water to quicklime, no size being added. It is an excellent germicide and insecticide. Whitewashing is quite different from limewashing. “Whiting,” i.e. finely-ground chalk, to which a certain proportion of size and alum had been added is mixed with water. The size and alum are added to prevent the whitewash from being rubbed off. Distempering is identical with whitewashing, except that pigments are added. It is distinguished from painting in oils, by the fact that the pigments are mixed with size, instead of with linseed-oil and turpentine. Painting in distemper is practically limited to plaster, which should first receive a coat of whitewash to diminish its porosity. Oil-paints are impervious, distemper is as absorbent as plaster or whitewash. Various washable distempers, as duresco, are made, which are more durable and non-absorbent. Water-glass consists of silicate of potash, which in the gelatinous form is soluble like size in hot-water, but when allowed to dry forms an impervious film. It can be used for protecting porous stone from the effects of weather; and renders internal surfaces of walls non-absorbent and washable.

Oil-painting renders wall-surfaces impervious, and enables them to be easily washed. The importance of this in the event of any infectious disease occurring, is obvious. The question arises whether distempered or papered walls, which are porous, or painted walls, which are non-porous, are preferable from the standpoint of health. The difference between the two is seen during damp weather, when moisture condenses and runs down the latter and is invisible in the former. In practice in domestic dwellings the former are preferred; but although some advantage is thus secured in ventilation through the wall-substance, there is the serious disadvantage that particles of dirt accumulate and may seriously interfere with the purity of the air of a room. Hence the importance of rubbing down the internal surface of a room, whether distempered or papered, at intervals with bread crumb or dough (see page [332]). This effectually removes all accumulations of dirt. A painted wall presents the enormous advantage that it can be frequently washed; while the loss of ventilation may be ignored, if windows and doors be properly utilised for this purpose. The presence of poisonous pigments in oil-paints is of importance to the workman, but not to the householder except during the painting, as paint, unlike distemper, does not rub off the wall. Lead is the chief poison present, as white lead (carbonate of lead). Various substitutes for lead paints have been introduced.

Painting wood or iron-work is valuable, not only as a preservative from the effects of the weather and the oxidising action of the air, but also because it tends, to a large extent, to prevent the absorption of organic matters; and its surface can be frequently cleansed.

Paper is the material most commonly employed for covering walls. It is more absorbent and retentive of moisture than distemper.

Light-coloured papers should be chosen, as they are more cheerful, and are not so likely to harbour dust. Glaring patterns are objectionable, as they tire the eyes. The paper should not present any surface-projection for the lodgment of dust.

In bathrooms and water-closets, the wall-surface should be non-absorbent. Paper, unless varnished, should therefore be avoided. The best covering for these places is glazed tiling, or painted cement.

Not uncommonly, a new paper is pasted over an old one; and this may be repeated several times. Under these circumstances dangerous dirt accumulates. Before new papering is put on, the walls should be cleared of all vestiges of the old, thoroughly washed down, and subsequently coated with size (that is, “clear coloured”). The sizing diminishes the absorptive power of the wall, and gives a good surface for applying the paper.

Bed-room papers require to be more frequently changed than those of other rooms. Bed-rooms in regular use should be re-papered at least every two years. It is still better to use distemper for such rooms, as this can be washed off in a few hours with comparatively little expense, and can be made of any tint desired.

Rooms in the basement should not be papered, as the walls require frequent washing down and cleaning. Here also a washable distemper colour can be used.

Various kinds of sanitary paper are now sold which are washable, and relatively non-absorbent. Some of them require varnishing; others do not. Such papers are certainly cleaner than ordinary paper; but it would not be safe to trust to their non-absorptive character. Lincrusta Walton is non-absorbent, and can be scrubbed with soap and water; but it is expensive. Other cheaper materials possessing the same properties can now be bought.

Arsenic in Wall-Papers and Paints has until a few years ago been a not uncommon source of prolonged ill-health—the cause of which has possibly not been detected until the illness disappears, when the offending room is vacated for a period. Arsenical pigments are now only rarely used for wall-papers. The symptoms produced vary greatly, and may closely simulate those of different diseases. In some cases repeated attacks of diarrhœa and abdominal pain occur. Or there may be nausea, headache, frequent griping pains, and loss of appetite. In other cases restlessness, loss of sleep, and general malaise are the chief symptoms, with the occasional addition of conjunctivitis (superficial inflammation of the eye). Out of 100 cases collected and reported on by a Committee of the Medical Society of London, diarrhœa, nausea, and intestinal mischief occurred in 85; severe depression in 16; conjunctivitis in 19; and cough, asthma, etc., in 9.

The severity of the symptoms produced will vary with the amount of arsenic contained in the paper, and the length of time daily that the patient is exposed to the fumes.

Some persons again are much less susceptible to the influence of arsenic than others. This will explain why some escape while occupying the same room in which others suffer severely. More commonly, however, the exemption is due to shorter exposure.

The most dangerous preparation occasionally employed in wall paper printing is Scheele’s green (arsenite of copper). Emerald-green—an aceto-arsenite of copper—is sometimes used to produce more delicate tints. Aniline dyes, especially the red, may contain much arsenious acid (white arsenic). The arsenic compound is made to adhere to the paper by size or some other material. When dry, it cracks and peels off, and minute particles get into the air as dust. In addition, arsenic compounds easily volatilise, and become diffused in a gaseous condition throughout the atmosphere of a room, even when its temperature is not greatly raised. The virulence of the arsenical colouring is in proportion to its volatility. Arsenic seems to be much more dangerous when associated with size. It has been shown that a mixture of white arsenic and starch paste, or other organic substance, leads to the formation of gaseous arseniuretted hydrogen, while this does not occur when no organic matter is present (Dr. Fleck). Distemper frequently contains arsenic, and as it also contains size, arseniurretted hydrogen is liable to be given off at any time. Size is largely used for fixing colour; thus, the proper conditions for the development of arseniurretted hydrogen—the most dangerous compound of arsenic—are present. As much as 17 grains of arsenic have been discovered in each square foot of a wall-paper. Now, arsenic is sometimes given internally for certain skin and other diseases, but the dose is only from 1 ∕ 60 to 1 ∕ 12 grain; the capacity for poisoning of such a paper as the above will therefore be evident.

Papers of other colours than green have been found to contain dangerous quantities of arsenic; thus blue, mauve, red, and brown may contain large quantities; the delicate greys often yield a considerable amount, and some white papers are heavily loaded with it. Arsenic is occasionally present in stockings and other wearing apparel, artificial flowers, toys, etc. In these cases, it may produce irritation of the skin, and even eczema.

The presence of arsenic may be detected by the following tests:—

(a) Reinsch’s test. A portion of the suspected paper (two or three inches square) is cut into small pieces, and placed in a good-sized test tube; water is added until the tube is about a third full and then one or two teaspoonfuls of pure hydrochloric acid, and a small piece of pure copper foil. If the test tube is now heated for a few minutes over a spirit lamp, arsenic, if present, will be deposited as a black or dark steel-coloured coating on the copper. A mere tarnish of the copper must not be accepted as evidence of the presence of arsenic, but an almost complete obliteration of the colour of the copper.

(b) Take the copper covered with arsenic, dry it, and then heat it in a perfectly dry test tube. Crystals of white arsenic, which may be identified under the microscope, will be deposited higher up in the tube.

(c) Marsh’s test. The ordinary apparatus for developing hydrogen by the action of diluted sulphuric acid on zinc is employed, the suspected paper being inserted in the bottle. The hydrogen coming off is burnt, and a clean porcelain surface is applied to the flame. If there is arsenic in it, it is deposited on the porcelain in a black patch.

Windows are required to open directly into the external air in every habitable room. The window area according to the model bye-laws of the Local Government Board and the London Buildings Act of 1894, must be at least one-tenth of the floor area, and half of this at least must be made to open. The following rules have also been given. (B = breadth, L = length and H = height of room.)

Area of window(B × L) ∕ 10 London Building Act
(B × L × H) ∕ 100Gwilt
√(B × L × H)Morris

In a room measuring 15 × 20 × 12 feet, the preceding rules would give a superficial area of window space of 30, 36, and 60 square feet respectively. Plate glass dissipates heat less quickly than sheet glass.

Objection may be taken to plate glass windows, in passing, especially for shops, banks, etc., in view of the fact that they are commonly made without any arrangement for ventilation (see also page [148]).

The hygienic necessities of Floors are that they shall be impervious to moisture and to dust. On the ground floor the ordinary arrangement is to provide a joisted and boarded floor raised about a foot above the ground. Dry rot is one of the dangers in connection with such boarded floors on the ground floor. The chief causes which tend to induce rotting, are damp walls, lack of ventilation, contact with mortar, damp earth, or vegetable mould, and worst of all, alternations of damp and dryness, or wet along with heat.

In order to avoid these dangers in connection with boarded floors, the ends of all timbers resting on walls should have a clear air-space around them, and communicate with the external air by means of perforated bricks. The larger timbers, girders, etc., should rest on stone templates, and the smaller joists on hoop-iron bonds. In all cases, the timber used should be well seasoned, and properly ventilated. The ends of oak posts, which are to be driven into the ground, should be charred, if the timber is old, or steeped in a solution of chloride of zinc.

The ends of the joists should be trimmed, so as not to come too near to chimney flues.

The best plan for flooring is to place an impervious flooring resting on the solid ground. This is more secure against rot than the boarded floor, and affords no space for dirt and vermin to lodge. Such an impervious floor may be formed of concrete over a layer of asphalte, as in the well-known terrazzo flooring. This is very suitable for corridors, pantries, etc. For living-rooms wood-block flooring is placed over the cement, molten pitch connecting the two. The blocks are 2 to 3 inches thick. If the wood is soft, as deal, it must be kept clean by washing; if hard, as oak or teak, it can be wax-polished. Parquetry consists of small pieces of hard woods carefully fixed and polished.

For upper floors the ordinary flooring is of floor-boards supported on wood joists, beneath which are wood laths and plaster. The floor-boards should be thoroughly seasoned, otherwise they will shrink, and the joints be filled with dirt. This dirt may accumulate for years between the floor and the ceiling of the room below, vitiating the air and helping to increase the stuffiness characteristic of dirty houses. Various plans are adopted for uniting the edges of floor-boards and preventing dust from dropping between the boards.

Fig. 41.
Tongued Floor.

The one most commonly employed is the ploughed and tongued floor (Fig. 41). In this, both edges of the floor are grooved so as to receive strips or tongues of iron or wood, an equal half of each strip being in the groove of each of two boards when they are in place. A less expensive method than the above is to splay the ends of the boards so that they slightly overlap each other. This is not so efficient as the above, but is much better than simply placing the boards side to side as is commonly done.

Solid wood floors resting on a bed of concrete are free from the risk of harbouring dust, and are relatively fire-proof.

Oak or teak in narrow boards, made with close joints, and then oiled and beeswaxed and rubbed to a polish, makes a good and almost non-absorptive floor. One of the best floors is made of concrete, with iron joists, and oak boards laid above this.

Carpets are commonly made to cover the entire floor of rooms. This cannot be too much deprecated. Carpets, like curtains, are mere dirt-traps, which become loaded with filth of every description. This is abundantly proved when a carpet is swept, and the dust allowed to settle on all the articles in the room. Such dust, if examined, will be found to consist not only of mineral matter, but also of every description of vegetable and animal impurities. The inhalation of such dust, which may contain particles of fæcal matter, as well as the dried expectoration from consumptive or other infectious patients, is a not infrequent cause of infection to healthy persons.

The substitution of a central carpet, for one covering the entire floor, is a great improvement.

The carpet should be easily removable, in order that it and the floor may be thoroughly cleaned at intervals.

In bedrooms, the less carpet the better. Good Chinese or Indian matting is serviceable, as it does not retain the dust and other impurities which are apt to become fixed in the woolly texture of the carpet. Oil-cloth, linoleum, and similar materials are in common use for covering halls, passages, etc. They are particularly useful in preventing dust from gaining access to the spaces between floor-boards.

The prevention of dust should be the great aim of the householder, as dirt frequently carries infection. Sweeping as ordinarily done scatters dirt over the room, and dusting with a dry cloth fails to remove it. Mechanical sweepers, in which the dirt is collected in a box are valuable. The best plan is to have movable carpets, roll them up for shaking or beating at a distance from any house, and wipe the boards with damp cloths. All wooden and leather furniture, picture frames, etc., should be wiped down with cloths rung out of water so as to be just damp.

[CHAPTER XXXIII.]
THE SOIL.

The Varieties of Soil.—The following facts summarise what is regarded as the relative healthiness of various sites for dwellings. The differences between different sites may, however, be reduced to a minimum by having the dwelling well above the ground-level and by protecting it from dampness.

1. Granitic, Metamorphic, and Trap Rocks usually form healthy sites for houses. The slope is generally great, and the ground consequently dry.

2. Clay Slate resembles the last in its effects on health. Water is, however, often scarce, owing to the impermeability of the rocks, and for the same reason occasional floods occur.

3. Limestone and Magnesian Limestone Rocks resemble the last in possessing considerable slope, so that the water passes away quickly. The hard oolite is the best formation under this head, and magnesian limestone the worst.

4. Chalk is a healthy soil when unmixed with clay, and permeable. Goitre is not so common as in limestone districts. If the chalk be mixed with clay, it is often damp and cold.

5. The Sandstones are healthy, soil and air being dry. If mixed with clay, or if clay lie under a shallow layer of sand-rock, the site may be damp. The hard millstone grit is a healthy formation.

6. Gravels of any depth are healthy, unless they are water-logged, as near rivers. Then a house on impervious clay may be drier than one on gravel.

7. Sands are healthy when of considerable depth; they may be unhealthy when shallow, and lying on a clay basis; or when the ground water rises through them from ground at a higher level.

8. Clay, Dense Marls, and Alluvial Soils generally, are apt to be cold and damp. Water is retained in them, and is often very impure. Thorough drainage improves a clay soil, and a house on a clay soil may be so constructed, as not to be damp.

9. Cultivated Soils are not necessarily unhealthy; but

10. Made Soils are always to be carefully avoided, as sites for houses. The materials with which inequalities have been filled up are commonly the contents of dust-bins, or some other refuse. The gradual putrefaction of organic matters renders the air about the houses impure. Such soils require free subsoil drainage, in order to keep them dry. It appears that the organic matters in soil are gradually removed by oxidation and bacterial purification. At least three years should be allowed before any such site is built on.

The following table places different geological formations in their order of healthiness for the purposes of a site (Parkes):—

PERMEABILITY
OF WATER.		EMANATIONS
INTO AIR.
1. Primitive rocks, clay slate, millstone gritSlight.None.
2. Gravel and loose sands, with permeable subsoilsGreat.Slight.
3. SandstonesVariable.Slight.
4. LimestonesModerate.—
5. Sands with impermeable subsoilsArrested by subsoils.Considerable.
6. Clays, marls, alluvial soilsSlight.Considerable.
7. Marshes, when not peatySlight.Considerable.

The general geological conditions have an important bearing on the choice of a site for a house in so far as they affect the local climate, and the difficulty of keeping the house warm and dry. Pettenkofer expressed this in his dictum, that we take holiday for change of soil, rather than for change of air. The character of a soil has an important influence on humidity, radiation, evaporation, and in fact most of the factors going to make up “climate.” The immediate local surroundings of a house (page [201]) have an even greater influence on its salubrity than the underlying geological formation.

The soil consists of mineral and organic matters. On the amount and character of the animal and vegetable matters (along with the condition of moisture and aeration), the healthiness of a given soil depends. The presence of vegetable matter, subject to alternate wettings and dryings, and to heat, has until recently been regarded as the condition on which malaria depends; but it is now known that malarial places owe their character to their being favourable to the growth of the larvæ of certain mosquitoes (page 307); and that drainage of the soil cures malaria by removing the ponds in which these develop. The two chief agencies at work to rid the soil of organic impurities, are nitrification and the influence of growing plants. The organic matters become oxidised into ammonia, nitrites, and nitrates, and these are eagerly assimilated by vegetation.

Nitrification is effected by micro-organisms in the soil. Ordinary garden mould and agricultural humus contain large numbers of micro-organisms. Their number diminishes with the depth of the soil, and below 12 to 15 feet there are few. Apart from the occasional presence of pathogenic (disease-producing) micro-organisms, the most important are those producing oxidation of organic matter, especially nitrification. This occurs at a less depth than 4 feet from the surface of the ground. The operation of these micro-organisms is necessary to convert sewage and other impurities into harmless nitrites and nitrates, and it is regularly going on in all normal soils. That the power of purification of sewage by soil is due to the micro-organisms in the latter, can be proved by the fact that when the soil is baked, it loses for a time its purifying power.

The Air contained in the Soil varies greatly in amount with the character of the soil, and with the level of the ground-water. As the ground-water rises, the ground-air is driven out. Thus, after a heavy rainfall a large proportion of this air will be displaced. Variations in barometric pressure, and a rise or fall of temperature, cause movements in ground-air. A house artificially warmed is liable to receive air from underground, unless means are adopted to make the floors impervious. The warmth of the house acts as an air-pump, aspirating the colder air into its interior. The air from cesspools or defective drains may be similarly aspirated into the house; and the same cause particularly explains the unhealthiness of houses built on “made soils”. Coal gas has occasionally made its way into houses when not laid on to them, by the gas escaping from leaky pipes in the street often following the track of water or drain-pipes until it is aspirated from beneath the house into its interior. This has resulted in one instance in an explosion, and in others in poisoning by the gas.

Fig. 42.

The occurrence of currents of air in soil may be illustrated by a simple experiment. In Fig. 42 B is filled with fine sand in which is imbedded the tube A with its open end F at the bottom of the sand C. The upper end of A is connected by the rubber tubing D with the U-shaped tube E, in which is inserted some coloured water. When the experimenter blows on the surface of the sand at A, the impulse passes through the sand up the tube from F, and deflects the water in the syphon bend at E.

The amount of ground-air varies greatly. Loose sands often contain 40 to 50 per cent., soft sandstone 20 to 40 per cent., and loose surface-soil many times its own volume.

The nature of the air is not accurately known. It is, however, extremely rich in carbonic acid, of which it contains from 1 to 10 per cent. or even more. The carbonic acid is derived from the organic matter in the soil, by the action of bacteria, in a manner analogous to nitrification.

The Water contained in the Soil is divided into moisture and ground or subsoil-water. When air is present in the soil as well as water, the soil is merely moist. Pettenkofer defines the ground-water as that condition in which all the interstices are filled with water, so that, except in so far as its particles are separated by solid portions of soil, there is a continuous sheet of water.

The Moisture in the soil varies in amount. Open gravel will absorb from 9 to 13 per cent. by weight of water; gravelly surface soil 48 per cent.; light sandy soils from 23 to 36 per cent.; loamy soil 43 per cent.; stiff land and clay soils from 43·3 to 57·6 per cent.; sandy and peaty soils from 61·5 to 80 per cent.; peat 103 per cent. (B. Latham). The moisture being derived from the rainfall on one side, and the ground-water on the other, will vary with the amount of these. Some soils are practically impermeable to water, such as trap or metamorphic rocks, unweathered granite, hard limestone, and dense clay; while others, such as chalk, sand, sandstone, vegetable soils are permeable. Commonly the metamorphic rocks and hard limestones present fissures, which render them pervious. The rainfall which does not penetrate the soil flows into the streams and rivers at once, or is re-evaporated. The amount of percolation of rainfall is estimated by an artificial soil-gauge. Most percolation and least evaporation of rainfall occurs from October to March inclusive. The difference between the percolation and rainfall is the loss caused by evaporation and vegetation.

The Ground-water forms a subterranean sheet of water, which is in constant motion. There is first of all, an irregular rise and fall of the water, according as it receives new additions from the rainfall, or loses a certain amount of its substance by percolation and evaporation; and there is, secondly, a constant movement towards the nearest water-course or the sea. Many towns derive their drinking-water from the ground-water, especially that in the chalk. Thus in Brighton there are no streams; but wells are dug in the South Downs about 150 to 180 feet deep down to the level of the subterranean water. Then long adits are tunnelled, parallel to the coast at or near the level of this water, which is thus intercepted on its way towards the sea, and pumped up to supply the town. In Munich, Pettenkofer reckoned the rate of movement of the ground water towards the outlet as 15 feet daily. It is impeded by impermeability, or a deficient slope of the soil. The roots of trees also greatly impede its flow.

The level of the ground-water is constantly changing (see Fig. 7). The alteration in level may be only a few inches either way, while in some parts of India it is as much as 16 feet. The level is generally lowest in October and November, highest in February and March.

A fall in the level of the ground-water may be due to a dry season, or to improved subsoil drainage. A rise in its level is due to an increase in the rainfall, or some obstruction in the outflow, as from a swollen river. The tide may influence the level of the ground-water at a great distance. A sudden alteration in the level of the ground-water is a common cause of floods in mines.

The distance of the ground-water from the surface may be only two or three feet, or several hundred feet, the difference being due to the varying level of the nearest impervious stratum of soil. Its distance below the surface of the soil can easily be measured by ascertaining that of the water of a shallow well in the neighbourhood. It should preferably not be nearer the surface than five or six feet. Sudden changes in the level of the ground-water from inundations render any soil unhealthy, and are even more objectionable than a persistently high level. This is especially true in the case of permeable soils. A sudden rising of ground-water expels the air in the soil, together possibly with particles which may comprise infectious material; it also washes similar impurities out of the subsoil, and carries them into neighbouring wells. Numerous epidemics have been traced to this source.

The Temperature of the Soil varies greatly with its geological character, as well as with the temperature of the atmosphere. The daily changes in the temperature of the atmosphere do not affect the soil beyond a depth of about three feet. The annual changes in the atmosphere will affect the soil in a varying degree, the amount being dependent on the character of the soil as regards conductivity and retentiveness for heat. Such annual variations do not penetrate below forty feet, and are very small below twenty-four feet. The temperature of the earth increases with its depth, the rate of increase in England being stated to be about 1° Fahr. for every 54½ feet.

In England the water of permanent springs has a fairly constant temperature of 49° to 51° Fahr., which is the temperature of the deeper part of the subsoil. The method of taking the daily temperature of the subsoil at a depth of 4 feet is described on page [240].

Although the average temperature of any soil depends on the climate, soils conduct heat in a very varying degree, and therefore absorb unequal quantities. This has an important bearing on the comfort of those living on a particular soil. Schübler’s experiments give the absorbing power of the chief kinds of soil, 100 being taken as the standard.

Sand, with some lime100·0
Pure sand95·6
Light clay76·9
Gypsum73·2
Heavy clay71·1
Clayey earth68·4
Pure clay66·7
Fine chalk61·8
Humus49·0

It is evident from this table that sand is very retentive of heat, while clays and humus are very cold. Green vegetation lessens the absorbing power of the soil, and radiation of heat is more rapid, evaporation occurring constantly from the herbage. The influence of trees on the temperature of the soil is considered on page [228].

Damp soils are colder than dry soils because of the evaporation going on. Buchan finds as the result of drainage of the soil, that (1) the mean temperature of arable land is raised 0·8° Fahr.; (2) cold is propagated more quickly through undrained land; (3) drained land loses less heat by evaporation; (4) the temperature of drained land is more equable, and (5) in summer is often 1·5° to 3° above that of undrained land.

Diseases Arising from the Soil.—The soil may be a cause of disease: (a) indirectly and (b) directly.

Indirectly a damp soil may cause disease by acting as a means of lowering the vitality of man and diminishing his resistance to disease. It is in this way that it has been credited with causing such diseases as neuralgia, catarrhs, and rheumatism. It is one of the elements in producing a climate unfavourable to health. As to rheumatism, see page [225].

Directly the soil may transmit the actual contagia (micro-organisms) of disease either by means of the subsoil water or its air. In the former case the disease-causing material gains access to the drinking water of wells, springs, or rivers; in the latter case it may be borne to the surface of the soil by currents of the ground-air or by insects, and then inhaled as dust, or gain access to food.

Certain disease-producing micro-organisms have been proved to be capable of living for some time in the soil. The chief of these found in the soil are the bacilli of tetanus (lockjaw), of anthrax, of malignant oedema, and of enteric (typhoid) fever. There are reasons for thinking also that the micro-organisms causing diphtheria, rheumatic fever, and epidemic diarrhœa, and possibly some other diseases, may occasionally live in the soil. In some diseases as enteric fever, cholera, dysentery and anthrax, the contamination of the soil can be shown to be derived from a patient suffering from the same diseases. In others, and particularly in tetanus, the same chain of evidence is obtainable.

(1) The conditions favourable to the production of malarial diseases have been generally considered to be the presence of a certain proportion of dead organic matter, the exposure of the soil to alternations of heat and moisture, with a limited access of air, and a temperature of at least 65°F. Though most common in marshy districts, and in recent alluvial soils, malaria may develop in connection with any geological formation. That it may be removed by drainage of the subsoil, is well known. The true nature of the connection between soil and malaria is stated on page [220].

(2) According to observations made by Pettenkofer in Munich, attacks of enteric (typhoid) fever are connected with fluctuations of the subsoil-water. He states his conclusions as follows:—

“Between the fluctuations of subsoil water and the amount and severity of enteric fever there is an unmistakable connection in this wise, that the total number of cases of and deaths from enteric fever falls with a rise of the subsoil water, and rises with fall of it; that the level reached by the disease is not in proportion, however, to the then level of the subsoil water, but only to the variation in it on each occasion; or in other words, that it is not the high or low level of the subsoil water that is decisive, but only the range of fluctuation.”

His observations have not been confirmed in this country; and the coincidence between excess of enteric fever and lowness of ground-water has been explained by the fact that under these circumstances the water in wells is low, and the area of drainage and the consequent risk of contamination are proportionately increased. There can be no doubt that the most common origin of enteric fever is from the infection of water or milk by infective matter from a recent case of the disease. This does not exclude the fact that enteric fever in this country is more prevalent in hot dry autumns, in which the ground-water is low. Probably under such conditions the contagium of the disease multiples more rapidly in the soil, in privies and other polluted places, and consequently the risks of infection of water and food as well of infection by dust carried from the contaminated spot are greatly increased.

(3) In regard to cholera, Pettenkofer holds similar views. He believes that the contagium of cholera can only be developed when there is a damp porous subsoil to receive the infected stools from a cholera patient; the damp porous subsoil forming a second host in which the poison of cholera must pass through one stage of its existence, before it is again capable of producing the disease. Such an essential relationship of the soil is not borne out by observations in India; and in England cholera has been repeatedly shown to be due to contamination of food (e.g. oysters) or water by the stools of preceding cholera patients, without the intervention of any agency of the soil.

(4) It has been repeatedly stated that a damp soil favours the prevalence of diphtheria. I have shown elsewhere, however, that this is not true, and that the greatest epidemics of diphtheria have occurred in exceptionally dry years, especially when several years of exceptionally small rainfall have succeeded each other; and have suggested that this may be associated with an intermediate stage in the life-history of the diphtheria-bacillus in the soil. A low ground-water and a comparatively high temperature of the soil go along with deficient rainfall, and would probably favour the multiplication of this bacillus in the soil.

(5) In rheumatic fever I have similarly shown that the supposed connection between damp soil and this disease is erroneous, the disease being most prevalent, both in this and other countries, in years of exceptional drought.

(6) Epidemic or Summer Diarrhœa has been supposed to have a special relationship with soil-temperature, Ballard having found that the summer rise in the mortality from this disease does not commence until the mean temperature recorded by the four-foot earth thermometer has attained somewhere about 56°F. The soil-temperature may be accepted as a convenient index of the conditions causing this disease. The disease I have elsewhere shown occurs most severely with a high temperature of the air and a deficient rainfall, and its fundamental cause is an unclean soil, the particulate poison from which infects the air, and is swallowed most commonly with food, especially milk.

(7) The close connection of consumption (phthisis) with a damp soil has been independently stated by Drs. Buchanan and Bowditch. Buchanan found that in the districts where improved sanitary arrangements had led to a drying of the soil, the death-rate from phthisis diminished; but where with sanitary improvements the soil was not dried, the death-rate from phthisis remained in one or two instances almost stationary. In Salisbury, Ely, Rugby, and Banbury, the death-rate from phthisis fell from 141 to 49 per cent. The amount of reduction in the death-rate from phthisis did not appear to be consistently proportional to the amount of drying of the subsoil. In a later investigation into the incidence of deaths from phthisis in the south-east of England, Buchanan came to the further conclusions that (a) there was less phthisis among populations living on pervious soils than among populations living in impervious soils; (b) less phthisis among populations living on high-lying pervious soils than among populations living on low-lying pervious soils; and (c) less phthisis among populations living on sloping impervious soils than among populations living on flat impervious soils. He, therefore, concluded that wetness of soil is a cause of phthisis to the population living upon it. (See also page [313]).

Drainage of the Soil.—There are two chief plans for rendering the soil drier—deep drainage and opening the outflow.

Subsoil Drainage should always be carried out by drains, separate from those for sewage. If the sewers are utilised for this purpose, their contents when full contaminate the surrounding soil. The subsoil drains should be composed of agricultural, i.e. unglazed, drain-pipes laid in towns in the same trench, but above the sewers, and they should discharge into the nearest water-course. If it is necessary to join them with a sewer, they should not pass directly into it, but into a disconnecting man-hole.

Opening the Outflow, in order that water may not remain stagnant in the soil, is occasionally required. This may be done by clearing water-courses, removing obstructions, and forming fresh channels.

The provision of sufficient surface-drains to carry off ordinary water and storm-water helps in drying the soil of urban districts.

Vegetation tends to diminish dampness of soil by causing rapid evaporation, and at the same time uses up the organic matter in the soil. Certain plants are more active in producing these effects than others: the Eucalyptus genus, including many species, and represented by the well-known blue-gum tree of Australia, is noted for its power in this respect; and the common sun-flower, which is very easy of cultivation, has a powerful influence in the same direction.

[CHAPTER XXXIV.]
CLIMATE AND WEATHER.

The Climate of a country has an important influence on the health and character of its inhabitants. The character of a climate depends on four main conditions:—

There are other conditions which are of subsidiary importance, but which have great influence in modifying the climate of any given locality. Thus:—

The Distance from the Equator is the most important factor in relation to climate. The sun’s rays become less powerful as they fall more obliquely, in travelling from the equator. This primary factor in producing climate is largely modified, however, by the relative distribution of land and water, and by the character of the prevailing winds of a district.

The Elevation of a locality affects the temperature and the barometric pressure, both falling as the height is increased. The amount of fall varies with the latitude of the place, with its situation in regard to surrounding districts, the degree of moisture of the air, the presence of winds, the hour of day, and the season of the year. It is usual to allow 1° Fahr. for every 300 feet of ascent above the level of the sea, and one-thousandth part of an inch depression of the barometer for every increase of one foot in height.

Hills, Plain and Valley.—The law of decrease of temperature with increase of altitude, is liable to great modifications, and even subversions, from various causes. The chief cause producing such modification of the law is the elevation in relation to the surrounding district. Thus, in the case of rising ground, the higher parts become rapidly cooled by radiation. The air here is likewise cooled by contact, and becoming heavier in consequence, flows down to low-lying ground. Hence places on rising ground are not so fully exposed to the intensity of frosts at night as places in the valley.

Valleys surrounded by hills and high grounds, not only retain their own cold and heavy air, but serve as reservoirs for the cold air falling from neighbouring heights. One finds, in consequence, mists in low situations, while adjoining eminences are quite clear.

The air of mountains is (1) cooler than that of lower districts with the exception already named. (2) It is less dense in proportion to the altitude; its pressure at the height of 16,000 feet being only half that at the sea level. (3) Its absolute humidity is decidedly diminished; there is some difference of opinion as to the relative humidity. (4) The air is as a rule purer. It is generally free from dust, and to a large extent aseptic (that is, free from microbes). (5) The amount of ozone is commonly greater than in lower regions. In addition to these characters, (6) the light is intense, and (7) the direct heat of the sun is greater, and the difference between sun and shade greater than in lower regions.

Owing to these peculiarities of mountain air, it is of great value as a restorative. The circulation of blood is increased, nutrition is improved, the chest expands, and the increase in its size may be permanent.

The presence of forests and sheets of water counteracts the effects of radiation from the earth. Thus if a deep lake fills the basin of a valley, the cold air descending from higher levels cools the surface water, which sinks and is replaced by warmer water from below. In this way deep lakes are sources of heat in winter, and places on their shores are free from the severe frosts which are peculiar to other low-lying situations.

If the slopes of a hill are covered with trees the temperature of its sides and base are considerably increased, as the trees obstruct the descending currents of cold air. The frosts of winter are felt most severely in localities where the slopes above them are destitute of vegetation, and especially of trees. It follows that in any given locality, the best protection against the winter cold is ensured by a dwelling situated on a slope a little above the plain or valley from which it rises, with a southern exposure, and sheltered by trees planted above it. Such local conditions should always be carefully enquired into, when a choice of site is possible, as the temperature of one part of a neighbourhood may differ by several degrees from that of another part near at hand. This is particularly important in the case of invalids.

Forests tend to modify a climate, and mitigate its extremes, whether situated on the slopes of mountains or on plains. In America, as elsewhere, the effect of destruction of forests has been to produce greater variation in the annual rainfall, to lengthen periods of drought, and to increase the power of floods and cloud bursts. Trees are heated and cooled by radiation like other bodies, but from their slow conducting power, the periods of their maximum and minimum temperatures are not reached for some hours after the same phases of the temperature of the air, and the effects of radiation are not confined to a small surface on the soil, but distributed to the level of the tree-tops. For these reasons, trees make night warmer and day cooler, thus giving to forest districts something of the character of an island climate. Evaporation occurs slowly from the damp soil beneath trees, as it is screened from the sun, and the trees prevent a free circulation of wind. Hence the relative humidity and rainfall are increased. At the same time forests mitigate the disintegrating effect of the rainfall on the soil.

Ground covered with Vegetation has a more uniform temperature than bare soil, the effect being much the same as that of forests, though on a smaller scale.

All growing vegetation evaporates a large quantity of water. A plant evaporates 200 pounds of water while it forms one pound of woody fibre; the effect of a forest must, therefore, be enormous. At the same time, vegetation, and especially trees, retain moisture in the soil. The water-supply of barren regions may be greatly increased by planting trees.

The absence of vegetation leads to extreme fluctuations of temperature. An extent of sand, for instance, raises the temperature of the air greatly during the day, as it is a bad conductor; but at night, radiation is very great, and the temperature falls accordingly.

Relation of Sea to Climate.—Water has the greatest specific heat of any known substance, being four times greater than that of the earth’s crust. On this account it takes longer to heat and to cool than the earth. Unlike the earth, likewise, it allows free penetration of the sun’s rays,—in clear water probably to a depth of at least 600 feet; consequently, the surface of the water becomes less rapidly heated. The freezing point of fresh water is 32°, while that of sea-water is 27·5°-28·4°. Thus, the sea remains open at a temperature at which inland lakes freeze, and has, therefore, a greater influence in moderating winter cold and summer heat. Another factor rendering it more competent to mitigate extremes of temperature than lakes, is the presence of currents, causing admixture of the water of different climates. Of these currents the most important for this country is the Gulf Stream, an immense stream of water which, when it leaves the Gulf of Mexico, is travelling at the rate of four to five miles an hour, and has a surface temperature of 88° F.

It is important to distinguish between the surface temperature and the deep-sea temperature, the latter being fairly constant. The whole of the depths of the sea is filled with water at or near 32° Fahr., which in the tropics is 40°-50° below the temperature of the surface-water.

The influence of seas on climate is so great as to lead to a classification of climates into oceanic, insular, and continental.

An oceanic climate is least liable to violent changes of temperature. It can only be obtained by a sea-voyage.

An insular climate presents smaller differences between the temperature of summer and winter than the interior of great continents, especially when the island is small and in the midst of the ocean. In the British Islands, the prevailing winds being westerly, places on the east coast are less truly insular than similarly situated ones on the west coast; and their climate approaches more nearly that of inland countries.

A continental climate is drier and more subject to extreme alternations of temperature than insular and oceanic climates.

Isothermal lines (lines of equal mean temperature) around the world bend up and down, the bendings being determined by the relative position of continents and oceans. New York has the same mean temperature as London, though New York is as far south of London as Madrid. This fact illustrates the fallacy in judging of the climate of a locality by the annual mean temperature. Means, it has been well said, are general truths but particular fallacies. One should know the extremes of temperature, and the extremes for each month of the year, as well as the amount and distribution of the rainfall, and the amount of sunshine, before judging of a local climate.

Winds are due to differences in atmospheric pressure caused by changes in temperature and moisture. Inasmuch as the temperature and degree of moisture of air vary with the prevailing winds, their consideration becomes very important. Winds bring with them the temperature of the air they have traversed: thus, in England, south winds are warm, while north winds are cold. Winds coming over an ocean cause less variation in temperature than those which have passed over an extensive tract of country. Thus, moist ocean winds are accompanied by a mild winter and cool summer, while dry continental winds cause the reverse conditions. The amount of moisture capable of being carried by a current of air increases with its temperature; therefore, equatorial winds become moister as they proceed, while north winds become drier. The south-west winds, in the British Isles, being both oceanic and equatorial, are very moist, while the north-east winds, being both northerly and continental, are peculiarly dry and parching.

Owing to the atmospheric pressure diminishing from the south of Europe northwards to Iceland, south-west winds are the most prevalent in Great Britain; and as this diminution of atmospheric pressure is greatest in the winter months, south-west winds are most common at this season. The result is that the temperature of these islands is higher than that due to mere latitude, and the temperature on the west coast is fairly uniform from Shetland to Wales.

Mountain ranges have an important bearing in determining the character of the prevailing winds. If the range is perpendicular to the direction of the winds, the latter lose the greater part of their moisture, and the places to leeward being exposed more completely to solar and terrestrial radiation (from comparative absence of aqueous vapour), winter becomes colder and summer hotter. The difference between the climates of the west and east parts of Great Britain is largely due to this cause. In Ireland, the mountains are not grouped in ranges running north and south, but in isolated masses, and the difference in climate between the east and west coasts is consequently less marked.

The prevailing winds have a great influence on the rainfall. (1) Thus if the wind has traversed a considerable extent of ocean, the rainfall is moderately large. (2) If a wind reaches into a colder region, its saturation point is lowered, and the rainfall is greatly increased; and if a range of mountains lies across its path, the rainfall on the side facing the wind is greatly increased, but diminished on the opposite side of the range. (3) If a wind after reaching land proceeds into lower latitudes or warmer regions, the rainfall is small, or absent. This accounts for the rainless summers of California, North Africa, and South Europe.

The Barometric Pressure varies daily, being at its maximum at about 9 a.m. and 9 p.m. The average range in the tropics amounts to 0·1 inch, but in this country does not usually exceed 0·02 inches. During the year the minimum barometric pressure usually occurs about the end of October, while the maximum is usually at the end of May or early in June. The ordinary variations in barometric pressure with changes of weather have little apparent effect on health; but more extreme changes produce marked effect. In mountain-climbing faintness and nausea may be caused at great altitudes. At the opposite extreme, in pier-driving and laying the foundations of bridges, men have to work in air-chambers at a pressure of from three to four atmospheres. Then what is known as “caisson disease” may be produced. The usual symptoms are discomfort or pain in the ears, giddiness, bleeding at the nose, vomiting, or even temporary paralysis. In such occupations it is most important that on leaving the air-chambers the atmospheric pressure should be gradually lowered.

The use of the barometer as a weather indicator is based on the fact that moist air is lighter than dry air. Hence, if the air is moist and rain imminent, the barometer falls rapidly. The maximum daily range in this country is rarely greater than 3 inches. Weather observations can be based on records kept at one spot. Their value is greatly enhanced, when such observations are compared with others distributed over a wide area. The wider the area from which such observations are collated, the more accurate the deductions that can be secured. If observations of places at which the barometrical pressure is identical be recorded on a map, we have a synoptic map, and the lines of equal barometrical pressure connecting these points are called isobars. The modern development of meteorology, enabling forecasts of weather to be made with approximate accuracy, is based chiefly on telegraphic communication of information, enabling isobars to be constructed.

It is found that isobars arrange themselves into seven chief forms (1) Cyclones. (2) Secondary cyclones. (3) V-shaped depressions. (4) Anti-cyclones. (5) Wedge-shaped isobars. (6) Cols. (7) Straight isobars.

Each of these varieties is shown in Fig. 43, which embraces the conditions in Europe, the eastern part of the United States, and over the North Atlantic on a certain day.

The closeness of the isobars, i.e. the rapidity of changes in atmospheric pressure determines the barometric gradient. The steeper this gradient, the greater the velocity of the wind in any given place. The distance between two isobars is equal to a change of a tenth of an inch in the mercury in the barometer. The direction of the wind in a given place is from the higher to the lower isobars. This is expressed in Buys Ballot’s law, which states that in the northern hemisphere, if you stand with your back to the wind, the lowest pressure is to your left and in front.

Fig. 43.
The Seven Fundamental Shapes of Isobars (after Abercrombie).

Cyclones or depressions are areas of low barometric pressure. A cyclonic system (Fig. 43) is formed by circles of concentric isobars. The differences between cyclones and anti-cyclones are as follows:—

Cyclones.Anti-cyclones.
Wind moves in the opposite direction to the hands of a watch.Wind moves in same direction as the hands of a watch.
Barometer is lowest in the centre.Barometer is highest in the centre.
Area comparatively small.Area comparatively large.
Gradient from centre to circumference steep.Gradient not steep.
Short duration.Long duration.
Velocity of wind great.Air comparatively quiet.
Weather bad; much rainfall.Weather fine.
Cool in summer; warm in winter.Hot in summer; cold and frosty in winter.

Cyclones usually travel from west to east, and are always associated with bad weather. The essential point in determining the character of the weather, both in cyclones and anti-cyclones, is the barometric gradient. Thus, according to the gradient, a cyclone may mean mild wet weather, a gale, or a hurricane. The turning point of a cyclone, just before the barometer begins to rise again, is called the trough. Cyclones are usually oval in shape, except in the tropics, where they are smaller and circular. The ordinary course of events in a cyclone is shown in Fig. 44, reading it from left to right.

In Secondary Cyclones, bad weather is usually associated with a stationary barometer and no wind. They are incompletely circular looped concentric isobars, with the lowest pressure in the centre. They frequently follow primary cyclones.

V-shaped Depressions are angular areas, with the lowest pressure in the centre, frequently forming between adjoining anti-cyclones (Fig. 43). In the northern hemisphere the tip usually points south. They usually move with great rapidity from east to west, and are always associated with squalls or thunderstorms. Their movement is very uncertain, and their forecast therefore more difficult than that of cyclones and anti-cyclones.

Fig. 44.
Weather Sequence in a Cyclone (after Abercrombie).

The tracing indicates the line which a self-recording barometer would have marked. The arrows mark the shift of the wind, and the number of barbs denote the varying force of the wind.

Anti-cyclones are associated with calm and cold in the centre, while on the borders the wind blows around the centre, spirally outwards in the direction of the hands of a clock. An anti-cyclone is usually accompanied by a blue sky, dry cold air, a hot sun, a hazy horizon, and little or no wind.

Wedge-shaped Isobars, unlike V’s, usually point north. They are areas of high pressure moving along between two cyclones, being really projecting parts of an anti-cyclone. The fine weather accompanying them is only temporary, because they are never stationary, and are generally followed by cyclonic disturbances. At the narrow end of the wedge thunderstorms or showers often occur, and at the wide end fog is common.

Cols or necks of relatively low barometric pressure occur between two anticyclonic areas. Like straight isobars they are intermediate systems. Over cols the weather is dull and gloomy; in summer they may be associated with thunderstorms.

Straight Isobars obviously do not enclose any area of high or low pressure. They form an intermediate condition, preceding the formation of a cyclone; and are usually associated with a blustering wind and hard sky.

Weather forecasting is necessarily somewhat difficult and uncertain. If one is dependent on observations at a single point the following rules are useful:—

The Thermometer also is of great value as a weather indicator, especially if one knows what is the average temperature at the place of observation for each day of the year. Thus:—

The veering of the wind in England is also useful as an indicator. Thus:—

The direction of the wind is an important factor. Thus:

Clouds give useful indications. Thus:—

A mackerel sky, that is, one covered with lines of cirrus clouds, causing halos around the sun and moon, presages rain in summer and thaw in winter. By degrees the light clouds descend and pass into either masses of cumulus, or into dense, horizontal stratus, which form at sunset and disappear at sunrise. Both these kinds pass into the grey, shapeless nimbus, which soon covers the entire sky and is followed by rain.

When numerous observations can be synoptically studied, forecasting becomes much more nearly certain. For this purpose telegraphic communications are indispensable. The continent of Europe is better placed than England for accurate forecasting. Areas of high pressure coincide usually with large areas of land, of low pressure with large surfaces of water. Thus England is placed near the boundary of the usual anticyclonic and cyclonic systems, and its chief disturbances come from the Atlantic from which early communication is impracticable. Furthermore cyclonic disturbances may be diverted from their course by a coastline or mountains or by the formation of an anticyclonic area. In view of these uncertainties, the large proportion of correct forecasts is somewhat surprising.

The Moisture of the Air depends upon the amount of vapour present in it, and the ratio of this to the amount which would saturate the air at the actual temperature. The former is called the absolute humidity, the latter the relative humidity. The dew point is the point at which condensation of some of the vapour in the atmosphere occurs, either as dew, rain, snow, or hoar-frost. The amount of moisture which the atmosphere can retain before such condensation occurs, varies with the temperature (see page [101]). Thus the air is drier at noon than at midnight, though the amount of vapour present in the two cases be the same; and it is for the most part drier in summer than in winter. This refers to the relative humidity, which is highest in cold weather. The absolute humidity is higher in summer than in winter; it varies more in continental than in maritime and insular climates; and there are daily variations according to the state of the sky, the movements of air, etc. The relative humidity is expressed as a percentage of what would be required to produce saturation at the given temperature. The usual relative humidity is 50 to 75 per cent. A moist air prevents excessive changes of temperature due to radiation. It protects the earth from too great intensity of the solar rays by day and from too rapid loss of heat by radiation at night. The inhalation of a dry air plays an important part in the cure of consumption. When the air is almost saturated with moisture, evaporation from the skin and lungs is diminished, and there is a feeling of oppression and disinclination to work caused by the interference with the tissue changes of the system.

Rainfall is caused by over-saturation of a column of moist air. This may be due to the contact of the air with a cold surface, as the ridge of a mountain or a large surface of water, or to the impact of a colder wind.

The amount of rainfall varies greatly. In some parts there is no rain, as in the desert of Sahara; while on the south-east slopes of the Himalayas, which are exposed to winds laden with moisture, it may be several hundred inches.

The latitude of a place has a great influence. As a rule the rainfall decreases with increasing distance from the equator; but local conditions may produce great modification, or even alterations of this law.

The elevation above the sea-level has a varying influence. In the Swiss Alps it is said that the rainfall increases with the elevation; but this rule does not hold good in America.

The nearness of large surfaces of water in summer tends to increase the rainfall, when water is colder than its surroundings, while in winter it has the opposite effect. The neighbourhood of the sea is for the west of England and islands adjacent, a cause of increased rainfall.

The influence of winds on the rainfall has been already considered. In Great Britain south-west winds more especially increase the rainfall. In their course they have travelled over the Gulf Stream and the general equatorial current, and have thus received warmth and moisture. The condensation of their moisture liberates a large amount of latent heat, thus raising the temperature of this country. In summer, however, south-west winds are cool and moist, as the Atlantic is not so hot as the continents of Asia and Europe over which other winds have travelled.

In England the average rainfall is about 33 inches, in Scotland 46, and in Ireland 38 inches. In the east of Great Britain, the rainfall is from twenty to twenty-eight inches. On the west coasts of Scotland and Ireland it is from 60 to 80 inches; and in some parts of Cumberland may be about 150 inches per annum. The annual rainfall varies greatly from the average for a number of years. In this country it has been estimated that the maximum annual rainfall exceeds by one-third, and the minimum annual rainfall is less by one-third than the average rainfall of a series of years.

The number of rainy days by no means corresponds with the amount of rainfall. There are fewest rainy days at the equator, where the rainfall is greatest. The rain diminishes the relative humidity of the air, and purifies it from dust.

[CHAPTER XXXV.]
METEOROLOGICAL OBSERVATIONS.

The Royal Meteorological Society recognises stations for the making and recording of observations of three kinds: (1) Second Order Stations, at which observations are taken twice daily at 9 a.m. and 9 p.m.; (2) Climatological Stations, at which the observations are taken once daily, at 9 a.m.; (3) Stations at which one or more elements only, e.g. rainfall, are observed. All instruments used should have been previously verified at Kew Observatory, so that the corrections for index error may be known.

The Barometer used should be of a standard kind. Five chief kinds of barometer are in use, only the last two of which are sufficiently accurate for scientific purposes.

1. The Dial or wheel barometer consists of a bent tube A B, the open end of which supports an ivory float B. This, as it rises and falls with the mercury, by means of the rack C turns a wheel, in the axle of which a needle is fixed. The needle turns in one direction, or the other as the mercury rises or falls (Fig. 45); the dial is divided by comparing it with a standard barometer. As the ordinary variations of the barometer are from 28 to 31 inches, the circumference of the wheel is made exactly 1½ inches, and thus the float B will rise or fall 1½ inches for a rise or fall of 3 inches in the barometer.

Fig. 45.

2. The ordinary syphon barometer (Fig. 46) consists of a bent tube attached to a piece of wood, and furnished with a screw v. The atmospheric pressure acts on the mercury at d, and the difference between the level of the mercury in the two arms of the syphon is the height of the barometer. To find the true height of the barometer the screw is turned till the shorter column stands at a opposite zero.

3. The aneroid barometer is made by exhausting the air from a small round metal box. This box is closed by a flexible lid of metal which, being elastic, yields to changes in the atmospheric pressure. To the lower end of the lid a spring is attached which runs downwards to the floor of the box and resists the atmospheric pressure. The movements thus produced by variations in pressure are magnified by a rack and pinion, and so communicated to a long index which moves over a graduated scale.

Fig. 46

Fig. 47.
Fortin Barometer.

a—Attached thermometer. b—Screw of vernier. c—Screw for setting level of cistern.

The standard Kew and Fortin barometers are both cistern barometers, the mercury in the inverted tube communicating with the mercury in a cistern below.

4. The Kew pattern barometer has a closed cistern below, the area of which being accurately known, the inches on the scale are not real inches, but inches of pressure, i.e. inches so shortened as to compensate for the rise of the mercury in the cistern. This compensation is necessary inasmuch as changes in atmospheric pressure affect the level of the mercury in the cistern as well as of that in the tube.

5. In the Fortin barometer (Fig. 47) the cistern has a pliable base of leather, which can be raised or lowered by means of a screw. The upper part of the cistern is made of glass, a piece of ivory indicating the zero of the scale. Before taking a reading, the level of the mercury must always be set exactly to this point by means of the screw. The Fortin is the most sensitive form of barometer, and the adjustment required in order to take a reading is easily performed.

To ensure more accurate reading of the barometer, a secondary scale or vernier is used, which slides upon the principal scale. This vernier is so graduated that 25 of its divisions correspond to 24 of the divisions on the fixed scale. The fixed scale is divided into inches, tenths (·1), and half-tenths (·05). Each division of the movable scale or vernier is therefore shorter than each division of the scale by 1 ∕ 25 of ·05, i.e. ·002 inch. Consequently the vernier shows differences of two thousands of an inch.

Method of reading Fortin’s Barometer.—First note the reading of the attached thermometer; next turn the screw at the bottom of the cistern, so that the ivory point just touches the surface of the mercury. Next adjust the vernier by means of the rack and pinion at the side of the barometer (Fig. 47) so as to bring its two lower edges exactly on a level with the convex surface of the mercury. In reading the barometer, first read off the division next below the lower edge of the vernier. In Fig. 48 this is 29·05. Then the true reading is 29·05 plus the vernier indication. Next look along the vernier until one of its lines is found to agree with a line on the scale. In Fig. 48 this is at the fourth division on the vernier. But each of the figures marked on the vernier counts as 1 ∕ 100 (·01), and each intermediate division as 2 ∕ 1000 (·002); hence the reading of the vernier will be ·008 inch, and the reading of the barometer 29·05 + ·008 = 29·058 inch. If two lines on the vernier are in equally near agreement with two on the scale, the intermediate value should be adopted.

Certain corrections are required in the actual reading for (1) index error; (2) temperature; and (3) height above sea-level.

The index error is found by comparison with a recognised standard at Kew. Correction for temperature is required. Every barometer has a thermometer attached, and the reading is reduced to the standard temperature of 32° F, by means of tables such as are given on page [32] of Marriott’s Hints to Meteorological Observers.

The height of the cistern of the barometer above sea-level should always be exactly obtained.

The correction necessary to reduce observations to sea-level (i.e. mean half-tide level at Liverpool), depends on the temperature and pressure of the air, as well as on the altitude. The data for this correction are given in Table III. of Marriott’s Hints.

Fig. 48.

Scale of Barometer (to Right) and of Vernier (to Left).

Thermometers.—The maximum thermometer may be on Negretti and Zambra’s, or on Phillips’ principle. In the former (Fig. 49) the bore of the tube is reduced in section near the bulb (A) in such a way that while the expanding mercury forces its way into the tube, the column of mercury breaks off on contraction, so that its upper limit shows the highest temperature that has been reached. The thermometer is set by holding it bulb downwards and shaking to make the mercurial column continuous. It is mounted in the screen horizontally (Fig. 51).

Fig. 49
Negretti and Zambra’s Maximum Thermometer.

The minimum thermometer chiefly used is Rutherford’s. It contains spirit in which is an immersed index (A, Fig. 50). With a falling temperature the spirit draws the index along with it; but on rising again, the spirit passes the index, leaving it at the lowest point to which it has been drawn. Thus the end farthest from the bulb registers the minimum temperature. The instrument is set by raising the bulb and allowing the index to slide to the end of the column of spirit. The thermometer must be firmly fixed and mounted quite horizontally.

Fig. 50.
Minimum Thermometer.

Thermometer Screen.—The above thermometers, as well as the dry and wet bulb thermometers are mounted in a Stevenson’s screen (Fig. 51). This is a doubled-louvred box through which the air can pass freely, but the sun cannot enter. The horizontal position of the maximum and minimum and the vertical position of the dry and wet bulb thermometers are shown in Fig. 51.

Three additional thermometers are usually included in a well-organised meteorological station.

A minimum thermometer placed on the grass gives the lowest temperature on the grass, which is often considerably lower than that of the neighbouring gravel walk. This record is chiefly useful for agricultural purposes.

Fig. 51.
Stevenson’s Thermometer Screen.

The earth thermometer chiefly used is shown in Fig. 52. It consists of a sluggish thermometer mounted in a short weighted stick attached to a strong chain, and of a stout iron pipe which is drawn out at the bottom to a point and driven into the earth, usually to a depth of 4 feet.

Solar radiation is measured by black-bulb and light-bulb thermometers in vacuo, which are mounted on a post 4 feet above the ground and record the maximum temperature.

Humidity in the air is measured by direct or indirect hygrometers. Of the former Dines’, Daniell’s, and Regnault’s are the best known, but as they are not used in observations acknowledged by the Royal Meteorological Society, the reader may be referred to their description in books on physics. The indirect hygrometer which is universally employed in this country is that furnished by the dry and wet bulb thermometers. In frosty weather they require much attention, and then a Saussure’s hair hygrometer may be used as supplementary. The general arrangement of the dry and wet bulb thermometers is shown in Fig. 53.

The wet bulb is covered with a single layer of soft muslin, while a noose of six to eight strands of darning cotton connects the neck of the wet bulb with a covered water receptacle 2 to 3 inches distant, below and at its side. This receptacle is kept filled with rain-water.

Fig. 52.
Symons’ Earth Thermometer.

Fig. 53.
Dry and Wet Bulb Thermometers.

From the readings of the dry and wet bulb thermometers three deductions can be made:

1. The temperature of the dew point.

2. The elastic force of aqueous vapour.

3. The relative humidity.

The dew point temperature is that temperature at which the outside air at the time the observation is taken will deposit the moisture contained in it. It is the temperature at which the air is saturated with moisture. It is calculated from the readings of the wet and dry bulb thermometers

(a) by Glaisher’s tables; (b) by Apjohn’s formula.

Glaisher’s tables are based on a series of numbers called Greenwich or Glaisher’s factors, which he determined by comparison between observations made with the dry and wet bulb thermometers and with Daniell’s hygrometer. The formula for using the factors is as follows:—

d = D - {(D - W) × f}

where d = dew point, D = dry bulb temperatures, W = wet bulb temperature, and f = factor.

The following examples are from Glaisher’s table of factors.

READING OF DRY BULB
THERMOMETER FAHR.		FACTOR.
55°1·96
56°1·94
57°1·92
58°1·90
59°1·89
60°1·88

The dew-point may also be obtained by Apjohn’s formula; which for a pressure of about 30 inches is F = f - (D - W) ∕ 87

The elastic force of aqueous vapour, i.e. the amount of barometric pressure due to the vapour present in the air is dependent upon the temperature of the dew-point. It is given for every tenth of a degree of temperature in Table VI. (p. 42) of Marriott’s Hints.

The relative humidity is a term expressing the percentage of saturation of the air with water vapour. It is obtained from Table VI. (above) as follows:—

Relative=Elastic force of water vapour at the temperature of the dew-point
HumidityElastic force of water vapour at the temperature of the air (i.e. the dry-bulb reading.)

In Table VII. of Marriott’s Hints, a table is given which enables the relative humidity to be found by mere inspection. Thus if the dry bulb temperature is 58°·5, wet-bulb 51°·7, and the difference 6°·8, the relative humidity given in the table is 62.

Fig. 54.
Snowdon Pattern Rain-Gauge.
A. Copper Upper Part of Gauge. B. Funnel. C. Bottle. To the right is shown the glass measure inverted.

The Rain-Gauge is best made of copper in the shape of a circular funnel, usually 5 or 8 inches in diameter, leading into a bottle underneath. It must always be set in an open situation away from trees, walls, and buildings. According to Scott no object ought to subtend a greater angle with the horizon than 20° in any direction from the gauge. The rain is measured by pouring the contents of the bottle into a glass measure, which is graduated to represent tenths and hundredths of an inch on the area of the gauge, the measure holding half an inch of rain on this area. Snow is melted before being measured.

Observations of wind should include its direction and force. The direction is observed by means of a well-oiled and freely exposed vane. There are 32 points to the compass, but a reading to eight points suffices. The force of the wind should be estimated by Beaufort’s scale, from 0 to 12. Thus:—

FORCE.MILES PER HOUR.
0. Calm3
1. Light air8
2. Light breeze13
3. Gentle18
4. Moderate23
5. Fresh28
6. Strong34
7. Moderate gale40
8. Fresh48
9. Strong56
10. Whole65
11. Storm57
12. Hurricane90

Robinson’s anemometer is also employed, but it is not altogether trustworthy.

Sunshine is recorded by the Campbell-Stokes burning recorder, and the Jordan photographic recorder. Of these the former is the more easily worked and gives more uniform results. It consists of a sphere of glass 4 inches in diameter, supported on a pedestal in a metal zodiacal frame (Fig. 55). The setting of the recorder should be due south, level from east to west, and with the axis of the ring inclined to the horizon at an angle equal to the latitude of the place, and so that the image of the sun, when the sun is due south, shall fall on the meridian line marked on the ring. The sun burns away or chars the surface of the cards inserted in the proper groove, and so gives a record of the duration of bright sunshine.

Fig. 55.
Campbell-Stokes Sunshine Recorder.

The amount of Cloud should be estimated daily, according to a scale ranging from 0 to 10, i.e. clear sky up to completely overcast. The form of cloud should also be stated, as cirrus, cirro-cumulus, cirro-stratus, cumulus, cumulo-stratus, stratus, and nimbus.

[CHAPTER XXXVI.]
PERSONAL HYGIENE.

Certain personal factors are very important in relation to health. The chief of these are constitution, temperament, heredity, idiosyncrasy, age, sex, and habits.

Constitution.—Health may vary in degree without the presence of actual disease. This fact is expressed by the use of such terms as “perfect,” “strong,” “feeble,” “delicate,” in speaking of the health of the same person at different times, and also as distinguishing one person from another. The constitution is an important factor in resisting disease, and a robust constitution may determine recovery from a severe illness, while the patient with a feeble constitution falls a victim to it.

The constitution of an individual is partly acquired, partly inherited. A feeble or delicate constitution may be acquired by unhygienic conditions, such as deficient exercise, the prolonged breathing of impure air, unhealthy occupations, some imperfection in diet, or dissipation.

But while many a robust constitution is enfeebled by such conditions, a weak constitution may happily be strengthened by careful and prolonged attention to the laws of health. This is especially well seen in the case of those who strengthen their muscular system by carefully-graduated and not excessive exercise.

Heredity has a great influence on health. As a rule the children of healthy parents are robust, and on the contrary, any “weak point” in the parents’ constitutions is liable to be participated in by their children. Both mental and physical conditions may be inherited. A peculiar habit of mind, as well as the same expression of features, may be inherited.

As regards physical diseases, the influence of parents is not less remarkable. The son of a gouty father requires to be particularly abstemious in order to avoid his father’s disease. Certain specific febrile diseases, e.g., enteric fever, diphtheria, and still more rheumatic fever, are hereditary in the sense that the members of certain families are more prone to them than others. Insanity, epilepsy, asthma, neuralgia, and hysteria are also hereditary in the same sense, and it is noticed that they occasionally alternate in different generations. Cancer, consumption, certain skin diseases, and a tendency to the early onset of degenerative diseases, appear also to occur more often in certain families than in others.

In most cases it is the tendency to disease which is transmitted, and not the disease itself. When an actual disease is inherited, as happens very rarely in tuberculosis and often in syphilis, the actual infection is transmitted before birth from the parent.

A peculiarity of form, character, or tendency to disease has been known to disappear in one generation and re-appear in the next; this variety of heredity is termed atavism. The evidence showing the inheritance of acquired characters, i.e. those which arise in consequence of the effect of external forces on the organism is not conclusive. Weismann believes that only those forces that influence the germ-plasm are inherited. It must be admitted that the instances of inheritance of acquired characters can be better explained otherwise. Thus the long neck of the giraffe was formerly explained on the supposition that the neck became gradually lengthened owing to the efforts made generation after generation in reaching food; but is better explained by Weismann on the supposition that those giraffes which, during times of famine were able to reach higher and obtain food from the twigs of trees would survive and pass on their characteristics to their young, while shorter necked giraffes would be exterminated.

The inheritance of proclivity to or immunity from attacks of infectious diseases is a problem of great difficulty; but there is no substantial reason for thinking that the efforts being made to diminish the prevalence of these diseases (including consumption) are likely to produce a weaker race or one more likely to suffer with excessive severity from these diseases should they be introduced after a long absence. (See also page [309]).

Temperament indicates a peculiarity in constitution, causing a liability to particular diseases, or to a special character in any disease to which a person becomes subject. Four temperaments are usually recognized—the sanguine, phlegmatic, bilious, and nervous, but unmixed specimens of these temperaments are rarely seen.

By idiosyncrasy is understood a peculiarity limited to a comparatively small number of individuals. Four varieties of idiosyncrasy may be described.

The first consists in an extreme susceptibility to the action of certain things, or an extreme lack of susceptibility. Thus most people at some time or other inhale the pollen of grasses, but only in a few cases does it produce that troublesome and distressing complaint—hay asthma. In certain persons a very minute dose of iodide of potassium produces distressing symptoms; in most cases these symptoms arise if the drug is taken for a prolonged period; but in a few cases it may be taken for an indefinite period without troublesome result. The case of a physician at Bath is very curious. The smell of hyacinths in bloom always made him faint away; so constant was this result, that before entering a room during the hyacinth season, he always asked the servant if there were any hyacinths in it.

The second form of idiosyncrasy consists in the production of poisonous results by common articles of diet. Thus some people cannot partake of shell-fish or lobsters without having severe nettlerash. In rare instances the smallest amount of egg, or in other cases mutton, or pepper, or some other substance will produce severe indigestion or nettlerash.

The third form consists in an inversion of the usual effects of certain substances, especially drugs. Thus opium in rare cases produces convulsions; while the aperient Epsom salts have been known to produce constipation.

A fourth form, that of mental idiosyncrasies, may be added, as where there is a strange preference or aversion for objects usually regarded as indifferent. Many cases of mental peculiarity, short of actual insanity, will come under this head; as will instances of depraved appetite for food, etc.

Age and Sex.—According to the period of life, danger arises from different sources. In infancy and old age extreme changes of temperature are especially dangerous, and additional protection is required (see also page [271]). Thousands of deaths occur in the first year of life, from substituting starchy foods for milk, the natural food for infancy and childhood (see page [303]). In childhood the danger from bad feeding is still present, and is evidenced by the frequency of rickets (page [28]); infectious diseases claim their thousands; and the disorders associated with dentition are common. In youth rapid growth is proceeding, and so the food must be abundant and nutritious. A proportionately larger amount is required than by an adult, as the functions of the body not only require to be carried on, but material is necessary to build up the growing tissues.

Manhood is the period of greatest stability of health. The health now depends on the use made of the previous periods of life, and on the habits acquired.

With the onset of old age come various degenerative diseases. The tendency is to death by gradual decay—a euthanasia or easy death, which is too seldom seen. Commonly, bronchitis or apoplexy or kidney diseases bring the scene to a somewhat premature end.

The mortality of man is greater than that of woman at all ages except 5—20.

Habits.—The immense power of habits in the formation of character is perhaps duly appreciated; but their influence on physical health is not so well appreciated; though it would be difficult to exaggerate it. The laws of health are as inexorable and unaltering as all other laws of nature; and whether broken through carelessness or ignorance, the Nemesis of disease inevitably follows. Whatever a man sows he reaps, in health as in other matters.

Habits are easily formed; but, when once formed, not so easily broken. They ought to be our servants; very commonly they become our masters.

In reference to eating and drinking, habits regular as to time and moderate as to quantity are especially important. The habit of eating hastily and masticating the food imperfectly, is certain, sooner or later, to produce disease. Over-eating, again, is a fertile source of disease, especially when the excess is in animal food. The amount of stimulation produced by a given dose of alcohol, gradually diminishes with its repetition; the consequence is, that in order to produce the amount of stimulation to which the system has become habituated, the stimulant requires to be gradually increased. The craving for stimulants is often a sign of ill-health, owing to disregard of hygienic laws or actual disease. Not infrequently it is due to badly-ventilated rooms or long hours of work without food, producing a sense of depression which food does not immediately allay. When the cause is unknown, recourse should be had to competent medical advice, and not to the brandy bottle.

Attention to the Action of the Bowels is a matter which is commonly neglected. The importance of a regular habit in this respect cannot be exaggerated; the bowels should always be relieved at a particular time each day. Where this does not occur the condition of constipation results. Owing to the retention of the fæces in the intestines beyond the normal period, the stomach and higher parts of the intestines do not perform their functions normally; indigestion and “dyspepsia,” accompanied by headache, flatulence, and other symptoms follow. Hæmorrhoids (piles) are another frequent consequence. At the junction of the small and large intestines is a dilated sac (in the cæcum). This becomes distended when constipation occurs; inflammation may be set up, and an operation required, or the condition is fatal. Powerful purgative medicines are injurious to the bowels, and they tend afterwards to increase constipation. It is better to take slow-acting aperient remedies, and better still not to take any at all, but relieve the condition by means of such articles of diet as stewed fruit, pears, figs, olive oil, or brown bread. As a rule more exercise is required in this condition, and always a prompt attention to the calls of nature.

[CHAPTER XXXVII.]
PERSONAL HYGIENE—EXERCISE.

Physiological Considerations.—In the strict sense of the word, exercise signifies the performance of its functions by any part of the body; thus, digestion is exercise of the stomach, respiration is exercise of the lungs, thinking is an exercise of the brain. But the term is usually applied chiefly to muscular contraction, and restricted to contraction of voluntary muscles. Involuntary muscles, which are concerned in the carrying on of the unconscious organic functions of life, are not directly controllable, and so their growth and state of nutrition cannot be regulated. There are two sets of involuntary muscle, which are of special importance—the heart and the muscles of respiration. The heart contracts at least sixty times per minute; the respiratory muscles contract about seventeen times per minute; and this amount of exercise goes on throughout the whole day. But although we cannot make our hearts beat quicker by a direct volition, and cannot breathe more rapidly than usual beyond a few seconds, yet a brisk walk will cause increased action of the heart and respiratory muscles, as well as a vigorous contraction of the muscles directly concerned in walking. Going uphill is a valuable exercise for the heart. The vermicular contractions of the intestines are to some extent also increased by voluntary exercise, through the indirect excitation of the whole system; thus, exercise is an important element in the treatment of constipation.

The muscles contain about a fourth of the whole blood of the body, and a very large share of the metabolism (page [4]) of the body occurs in them.

Hence the importance of keeping them in a healthy condition by exercise. The great danger is of not equilibrating the muscular and nervous functions. The ideal condition is where neither mental nor muscular culture is neglected, but both are co-ordinated to the production of a healthy man.

Effects of Healthy Exercise.—1. The Nutrition of the Muscles is improved. The volume, density, and energy of the muscles are increased.

2. The action of the lungs is increased. Dr. E. Smith found that if the air inspired while lying down be represented by unity, the amount inspired when erect is 1·33; when walking at the rate of one mile per hour, 1·9; at four miles per hour, 5; at six miles per hour, 7; riding on horseback, 4·05; swimming, 4·33. Or, putting it in another way, under ordinary circumstances a man inspires 480 cubic inches per minute; if he walks four miles per hour, he inspires 2,400 cubic inches; if six miles an hour, 3,260 cubic inches.

At the same time the amount of carbonic acid expired is increased. Its amount bears a nearly constant relation to the amount of muscular exercise, and consequently the amount of carbonic acid eliminated in various forms of exercise affords a just estimate of their relative value. The increased elimination of carbonic acid, the corresponding increased absorption of oxygen, and the absence of increase of elimination of urea are shown in the following summary of observations by Pettenkofer and Voit:—

ABSORPTION OF
OXYGEN IN GRAMMES.		ELIMINATION IN GRAMMES OF
CARBONIC ACID.WATER.UREA.
Work day9551284204237·0
Rest day709 912 82837·2

The above amounts are for the entire day. During actual exercise the excess of elimination of carbonic acid is much greater. Thus, Dr. E. Smith experimentally found that if the amount of carbonic acid eliminated during rest be represented by one, the amount walking at two miles an hour and carrying 7 lbs = 1·85, the amount walking at three miles an hour = 2·64.

Alcohol diminishes the excretion of carbonic acid, and should therefore be avoided during muscular training.

By muscular exercise the size of the lungs is increased, and their vital capacity, that is, the amount of air capable of being expired after a forced inspiration, is considerably increased. Corresponding with this increase of vital capacity, exercise, especially that in which the arm and chest muscles are systematically developed, increases the size of the chest. A perceptible difference in the circumference of the chest may be noticed after only a few weeks’ methodical exercise.

3. The action of the skin is increased.—Sensible perspiration is commonly induced, but less readily in those habituated to hard work. Insensible perspiration is always increased.

4. The temperature of the body is not increased, so long as perspiration occurs. Every muscular contraction involves the production of heat; but this is counteracted by increased evaporation from the skin, and by the circulatory current carrying the hotter blood to every part of the body, and so rapidly equalising its temperature. Chilblains are due to the defective circulation of the blood, and can in most cases be cured by active exercise aided by warmer clothing and an abundant supply of oxidisable food.

5. The Heart and Blood-vessels.—By exercise the heart’s action is increased in frequency and force. The pulse usually increases from ten to thirty beats per minute above the rate while at rest. After prolonged exercise it may temporarily fall below the normal standard.

6. The Digestion and assimilation of food are aided by exercise, especially when taken in the open air.

7. The nervous system is improved in nutrition and power by a moderate amount of exercise. In fact, a certain amount of muscular exercise is essential for a healthy mind.

8. The elimination of urea is not increased by exercise. Evidently then it is not the metabolism of the nitrogenous substance of the muscles which supplies the energy for muscular contraction; but of the other oxidisable and non-nitrogenous substances (such as glycogen and sugar) contained in them.

In practice it is found that with exercise more nitrogenous and non-nitrogenous food are both required.

Effects of Excessive Exercise.—After prolonged exertion muscles become exhausted. This is associated with an accumulation in the muscles of the products of their action (especially sarcolactic acid). Then rest becomes necessary, in order that the effete products may be removed, and the nutrition of the muscles restored.

Long-continued over-exertion produces chronic exhaustion, which may, if excessive, cause wasting of muscles. Exhaustion is much more liable to occur when a small group of muscles are exercised out of all proportion to others. Thus, in clerks, we have what is known as the writer’s or scrivener’s palsy. The muscles of the hand, and especially of the thumb, cease to respond to the volition of the writer, but are seized with spasm every time writing is attempted; and the muscles of the thumb tend to waste. A similar condition sometimes arises in violinists, tailors, etc. The practical inference from these facts is, that one group of muscles should not be exercised disproportionately to the muscles of the rest of the body, and that proper intervals of rest should be allowed.

Excessive exercise of the whole muscular system is very apt to harm those of previously sedentary habits. A walking tour entered on with more zeal than discretion, and not taken by easy stages for the first few days, is often productive of more harm than good.

In the intervals of great mental labour, as with students, the amount of exercise should not be suddenly increased, but should be regular and moderate in amount.

Competitive exercise should be strictly regulated. The Oxford and Cambridge crews have been said to acquire heart-disease more commonly than the average, but this is not correct. Hypertrophy of the heart may occur as the result of severe exercise, and this within certain limits is not an abnormal condition. Occasionally dilatation of the heart has been produced in weakly lads.

Amount of Exercise Desirable.—According to Parkes, the average daily work of a man engaged in manual labour in the open air is equivalent to the work involved in lifting 250 to 350 tons one foot high; this is a moderate amount, 400 tons being a heavy day’s work. The amount of muscular exercise involved in this may be easily known by remembering that a walk of 20 miles on a level road is equivalent to about 353⅔ tons lifted 1 foot; and that a walk of 10 miles while carrying 60 lbs. is equivalent to 247½ tons lifted 1 foot. (Haughton).

The amount of work done by a healthy adult per diem is stated by M. Foster to be about 150,000 metre-kilogrammes (i.e., 150,000 kilogrammes lifted 1 metre). Metre-kilogrammes can be converted into foot-pounds by multiplying by 7·233; into foot-tons by multiplying by ·003229; 150,000 metre-kilogrammes therefore equal 484·35 foot-tons. This is considerably in excess of Parkes’ estimate, but in certain laborious occupations this high amount is reached.

In addition to this amount of external work, there is the internal work of the heart, muscles of respiration, digestion, etc. This is estimated by Parkes at about 260 foot-tons.

The internal and external muscular work of the body together amount to about 1 ∕ 7th to 1 ∕ 8th of the total force obtainable from the food.

Every healthy man probably ought to take an amount of exercise represented by 150 tons raised 1 foot, which is equal to the work done in walking 8½ to 9 miles on a level road. A certain amount of this exercise is taken in performing one’s daily work; but apart from this, out-door exercise should be taken equivalent in amount to a walk of five or six miles. It is impossible to lay down rules to suit all cases, but a less amount of exercise than that named is probably incompatible with perfect health.

Effects of Deficient Exercise.—The muscles themselves become enfeebled and wasted. Some wasting of muscle occurs after a few days’ confinement to bed; and a limb confined in a splint speedily loses its healthy, rounded contour. Oxidation processes are diminished; less carbonic acid is eliminated, and it tends to accumulate in the system, owing to the diminished activity of respiration. In consequence of the diminished oxidation, the temperature of the body is not well maintained, and the heat is not uniformly distributed. Cold feet are a common complaint of those who lead sedentary lives, though seldom complained of by others.

Along with the other muscles, the heart becomes enfeebled and the circulation less perfect. Digestion is enfeebled; the appetite is poor. The nervous system also suffers; nervous irritability is a common result, while sleeplessness—a thing almost unknown among those who live by the sweat of their brow—is becoming much more common among the worried and ill-exercised inhabitants of our towns.

Many diseases are favoured by deficient exercise, and can be averted by systematic exercises and the concomitant increased supply of pure air. It is often difficult to appraise the relative merits of exercise and pure air; but there can be no doubt that both are of extreme importance.

The prevention of consumption, even in those with a strong hereditary tendency, is greatly helped by systematic exercises, especially those directed to the expansion of the chest cavity. In cases of consumption there is commonly a history of deficient exercise or an occupation involving a cramped position, as well as of living in an impure air.

Various deformities are induced by defective exercise of particular groups of muscles. Thus drooping shoulders may be caused by shoulder-straps confining the action of the shoulder-muscles in the earlier years of life. Stooping is favoured by sitting in cramped positions in school, and by the use of desks not inclined at the proper angle. Lateral curvature of the spine is due to weakness of the muscles of the back, and is best treated in its earlier stages by gymnastic exercises specially directed to strengthening these muscles. The tendency to such curvatures is greatly increased in girls by the fact that their trunks are imprisoned in corsets as if in splints, and so exercise of the trunk muscles is reduced to a minimum.

Rules respecting Exercise. 1. The clothing during exercise should not be excessive, and should not interfere with the free play of the limbs, nor with full expansion of the chest. Flannel is the best material to wear next the skin, as it absorbs perspiration without becoming non-porous.

2. Avoid chill after exercise. It is well, if there has been any perspiration during exercise, to strip and scrub the skin, particularly about the chest and arm-pits, with a rough towel.

3. Exercise should be systematic and regular. It is important to avoid sudden, violent, and competitive exercise. No severe exercise ought to be undertaken without a gradual training.

4. The amount of exercise must be regulated by individual fitness. A chain is no stronger than its weakest link. The muscles may be stronger than the heart or lungs, and the latter may be fatally injured by an amount of exercise which the muscles can well bear. Hence the importance of ascertaining the condition of the vital organs before entering on a course of training.

Another important bearing of this rule is in relation to the exercise of growing boys and girls. When we remember that a boy at school will sometimes grow six to eight inches in a year, it is evident that much energy is being expended in this direction, and that excessive gymnastic exercise can only do harm. Between the ages of fifteen and seventeen there is usually the greatest amount of physical development, and if there is great muscular strain at this period, growth is interfered with, and the power of resistance to disease may be seriously lowered.

5. Every part of the body ought to be exercised. This is done spontaneously by the infant. Every muscle of his body acts in sheer delight. The evils of exercise confined to particular groups of muscles have been already described. Lawn tennis is very valuable as affording exercise for both limb and trunk muscles.

6. Exercise should not be taken immediately after meals, as thus digestion is interfered with.

7. Exercise should be taken, as far as possible, in the open air. A small amount of exercise out of doors is much more invigorating than a large amount indoors.

The Forms of Exercise taken may be divided into recreative and educational, though both of course may be recreative under many circumstances.

The primarily recreative exercises, such as rowing, cricket, football, tennis, hockey, will, it may be hoped, be never replaced by educational gymnastics, though the latter possess a high value. The recreative influence as well as the influence on the power of self-control of such games as cricket and football render them of national importance.

Educational gymnastics can be applied to exercise the muscles of any part of the body, and can be exactly graduated to individual requirements. Singing, speaking, and reading aloud, are forms of muscular exercise very much neglected, and they are particularly important, as the lungs and voice are by these means greatly strengthened, and rendered much less liable to the inroads of disease.

Professor Haughton has shown that the work done by a man walking on a level surface at the rate of three miles an hour is equivalent to raising his own weight, plus the weight he carries through 1 ∕ 20 of the distance walked.

then we obtain by the following formula the amount of work done, the co-efficient of traction being multiplied by 2,240 (the number of pounds in a ton) to obtain the result in foot-tons.

(W + W1) × D ∕ (C × 2,240)

In ascending a height, a man raises his whole weight through the height ascended.

A regiment of soldiers marches ten miles, each carrying a weight of 60 lbs. What amount of work is performed by each soldier?

If we assume the average weight of each soldier to be 150 lbs., and that the march was at the rate of three miles an hour, then—

(150 + 60) × 10 × 5,280 ∕ (20 × 2,240) = 247·5 foot-tons.

In this example it is assumed that the march is on entirely level ground that all weights are carried in the most convenient manner, and that the rate of travel is three miles an hour. Velocity is gained at the expense of carrying power. It has been found that the amount of work is generally inversely as the square of the velocity. Haughton has determined from Weber’s calculations the co-efficient of resistance for three velocities.

VELOCITY.CO-EFFICIENT OF TRACTION
OR RESISTANCE.
1·818 miles per hour1 ∕ 28·27
4·353 miles per hour1 ∕ 13·70
10·577 miles per hour1 ∕ 7·51

Parkes has extended these calculations to show the distance in miles required to be travelled at various velocities to do work equal to 300 foot-tons, and the time required in each instance.

VELOCITY IN MILES PER HOUR.CO-EFFICIENT OF RESISTANCE.DISTANCE FOR MEN OF 156 LBS. TO EQUAL 300 FOOT-TONS.TIME REQUIRED IN HOURS AND MINUTES.
21 ∕ 26·7412·2hrs.
10		mins.
36
31 ∕ 20·5916·3524
41 ∕ 16·7413·3318
61 ∕ 12·189·6136
81 ∕ 9·607·6057
101 ∕ 7·896·3038

The co-efficient 1 ∕ 20, corresponds very nearly to 3·1 miles per hour, and it appears that at this rate of travel the greatest amount of work can be done with the least expenditure of energy.

How much work is done by a man weighing 150 lbs. who walks 15 miles up an incline 1 in 200?

The number of feet ascended in 15 miles

= 5,280 × 15 ∕ 200 = 396.

The amount of work done by the man in raising his own weight 396 feet high

= 396 × 150∕ 2,240 = 26·5 foot-tons.

The amount of work done in walking 15 horizontal miles at the rate of 3 miles an hour

= 150 × 15 × 5,280 ∕ (20 × 2,240) = 265.2 foot-tons.
Total amount of work done = 265.2 + 26.5 = 291.7 foot-tons.

Eight palanquin bearers carry an officer weighing 180 lbs. and a palanquin weighing 250 lbs., a distance of 25 miles. Assuming that each man weighs 150 lbs., what amount of work was done by each man? (Parkes.)

This being the total work done, the work per man = nearly 600.3 foot-tons.

A hill-coolie weighing 150 lbs. goes 30 miles with an ascent of 5,500 feet in three days, carrying 80 lbs. in weight. What is the work per day? (Parkes.)

Work of the ascent = (150 + 80) × 5,500  ∕  2,240 = 564·7 foot-tons.

Work of 30 miles walk = 230 × 30 × 5,280 ∕  (20 × 2,240) = 813·2 foot-tons.

Total work = 564·7 + 813·2 = 1,377·9.

Total work per day = 1,377·9  ∕  3 = 459·3 foot-tons.

Suppose a man weighing 150 lbs. in his clothes, carries a load of bricks weighing 35 lbs. up a perpendicular ladder 30 feet high, 100 times daily, what amount of work does he do; and what will it equal in miles walked upon a flat road at the rate of 3 miles an hour?

Suppose a man strikes 12,000 strokes in 5 hours with a 14-lb. hammer, raising it at each stroke 4 feet, how much work does he do? Compare this with a walk of 15 miles on a level ground at 3 miles an hour, the weight of the man and what he carries being 180 lbs.

The two amounts of work are related as 300 : 318·2.

[CHAPTER XXXVIII.]
PERSONAL HYGIENE (continued)—REST AND SLEEP.

Physiological Considerations.—Life is made up of alternations of rest and action. The exercise of any organ is followed by a necessary period of repose, during which the oxidised materials produced by functional activity are removed by the blood, and carried to the excretory organs; while at the same time fresh nutritive material is supplied by the blood to make good the losses thus sustained.

The only apparent exceptions to this rule of alternation of rest and exercise are the heart and lungs, and some less important organs acting out of the control of personal volition. But even these organs obey the universal law. The difference is that their rest is very frequent and momentary; the heart having to contract sixty or seventy times per minute, rests 6 ∕ 11 of a second each second, or more than thirteen hours in the twenty-four. The lungs and respiratory muscles rest a shorter time than this, but probably about three hours per day.

The necessity for rest is well shown by the sense of taste. If salt is kept in the mouth for a considerable time, the power of tasting it disappears, and only returns in its original strength after several hours. The gustatory nerve has been exhausted.

The other sense-organs illustrate the same principle. Persons are not uncommonly made deaf by the sounds of machinery. After looking at a particular colour for some time, the nerves receiving impressions from this colour are exhausted, and only its complementary colour is visible.

Rest may be either partial or general.

The principle of partial rest has very useful practical bearings. Such rest is illustrated by the student who takes a walk, or uses methodical gymnastic exercises; a concert may provide agreeable exercise for the auditory nerves and the part of the brain connected with them, while allowing the over-tired intellectual part of the brain to rest in peace; similarly, light literature may prove a pleasing rest after severer studies.

Walking is more especially the exercise of the brain-worker.

Partial rest is the same thing as change of occupation, and by a careful regulation of the relative amount of cerebral and muscular work, energy can be largely economised. The horse, which exercises chiefly his muscles, requires only five or six hours to recuperate his energy; and our muscles require less sleep than our brain.

Sleep is the only form of complete and general rest. In attaining this condition, the muscles sleep first, then the eyes close (owing to muscular rest), and the thoughts wander; hearing is the last sense to lose cognizance of the surrounding world; dreaming succeeds wandering thoughts, and even dreaming may cease if the brain repose is complete.

During sleep the brain diminishes in size, and becomes paler; the amount of blood in the brain being diminished. Probably the cerebral anæmia is rather a consequence of the functional inactivity of the brain during sleep than a cause of the sleep.

During sleep the heart and lungs continue their work; the blood is circulated and purified, the intestines continue their vermicular contractions, and absorb food from the alimentary canal, and the organs nourish themselves at leisure.

Two facts relating to sleep have important practical bearings. First, during sleep metabolism is less active, and so the temperature of the body tends to be somewhat lowered. Secondly, assimilation is more energetic; this favours the absorption of noxious vapours, if any are present. There is probably, therefore, slightly less danger of remaining in a stuffy, impure atmosphere during the day than at night.

Practical Rules Concerning Sleep.—1. Amount of sleep required. It is impossible to lay down any fixed rule applicable to all persons and circumstances. The amount of sleep required, like the amount of food, varies greatly.

Habitual deficiency of sleep produces a condition of wretchedness and prostration, with great restlessness. Prolonged watching inevitably breaks down the constitution. Not the least evil consequence of irregular and deficient sleep is, that sleep, when desired, is often courted in vain.

Habitual excess of sleep produces a condition of brain less active than usual, and less favourable for thought and action. Impressions are received less readily, and the power of will is correspondingly diminished.

The amount of sleep required varies with—

(1) Age.—The infant, if healthy, spends the larger part of his existence in sleep; gradually the amount required diminishes until, for the adult, seven or eight hours suffice. Children over two or three years old require sleep only during the night. In advanced life there is a tendency to revert to infantile habits, sleep occurring in frequent short snatches.

(2) Sex.—Women have been stated to require rather more sleep than men, but this is doubtful. The hours of sleep required have in accordance with this view been stated to be, “Six for a man, seven for a woman, and eight for a fool.” A reversal of this order would more nearly approximate to the requirements of town life.

(3) Temperament.—Those of a cold lymphatic temperament require more sleep than sanguine or nervous people, though the latter sleep more deeply. Frederick the Great, John Hunter, and Napoleon I. are said to have required only five hours’ sleep per day; but the last of these had the faculty of taking short naps at a few moments’ notice.

(4) The sick and convalescent require much more sleep than those who are healthy.

(5) Habit has a very important influence. Many people appear to sleep too much, and thus dull to some extent their mental faculties; but on the other hand, modern life, with its nervous strain, keen competition, and constant hurry and worry may make a larger amount of sleep necessary than that required by our forefathers, who invented the foregoing proverb.

(6) Occupation.—Mental work requires more repose than physical.

2. Relation of sleep to food.—The molecular life of the tissues—that is, the processes of nutrition—ought to be undisturbed. These go on most perfectly when no active function, such as that of digestion, is being performed. But while the stomach carries on the digestive functions to only a small extent during sleep, the intestines continue still to digest and absorb food. In accordance with these facts, it is advisable to allow at least two hours between the last meal of the day and sleep, especially if animal food has been taken.

3. As absorption is increased and the temperature is lowered during sleep, it is important to sleep in pure air, and to have warm coverings, especially about the shoulders and arms. Many an obstinate cough might be cured by the simple expedient of wearing a flannel jacket at night.

4. Sleep during the night and not during the day. It should hardly be necessary to say this, as the universal instinct of animals shows its advisability; but, unfortunately, the habits of mankind have commonly led to a partial reversal of the natural arrangement.

5. The room should be dark; light, like sound, is inimical to sleep. The head should be moderately raised. The temperature of the room for robust persons need not be artificially raised.

Sleeplessness, as a rule, occurs only when some physiological law has been broken. To relieve it, it is essential to equilibrate muscular and mental functions. Increase of muscular exercise is an important element in its treatment. In addition it is advisable not to have any severe mental work during the evening, nor to indulge in late suppers. Sleeplessness is the bane of many men of a nervous temperament, and chiefly attacks those of sedentary habits. It is apt to recur, and for this reason, if for no other, narcotics ought to be scrupulously avoided. The habit of taking such soporifics is unfortunately becoming much more common, and is productive of many evils. Death from accidental overdose is a frequent calamity; and, apart from this possibility, the invalid’s nervous system is completely ruined by persistence in the habit, his power of will is annihilated, and he becomes the miserable slave of an evil habit, whose end is death (see also page [54]).

[CHAPTER XXXIX.]
PERSONAL HYGIENE (continued)—CLEANLINESS.

Physiological Considerations.—The skin consists of a superficial part or epidermis, and a deeper part called the dermis or cutis.

Tubes of two kinds open on the surface of the skin, penetrating at their deeper ends into the cutis, viz. sweat or sudoriparous glands and sebaceous glands. The sudoriparous glands are simple tubes, the lower ends of which lie coiled up in the dermis. Each tube when straightened out is about a quarter of an inch long. It has been estimated that in the palm of the hand there are 3,528 orifices of sudoriparous and sebaceous glands on a square inch of surface; reckoning each gland at ¼; inch long, this means 73½ feet of tubes in this small space. Assuming that there are 2,800 tubes to every square inch, and that the amount of surface in a man of ordinary height and bulk is 2,500 square inches, it follows that there are seven million pores in a man—that is, 1,750,000 inches, or nearly twenty-eight miles.

The perspiration secreted by the sudoriparous glands is constantly evaporating from the surface of the body. It is very important that the orifices of these glands should be kept open in order that the secretion may not be interfered with. Animals have been killed by covering their skin with gelatine, and so preventing the escape of perspiration.

The sebaceous glands are shorter than the sudoriparous, and commonly end alongside the hairs before the latter issue from the skin. They secrete an oily material which serves the purpose of a natural pomade. The sebaceous secretion also keeps the general surface of the skin unctuous and supple. The smell of the sebaceous secretion may be unpleasant, especially in the arm-pits and some other parts. Frequent washing is therefore desirable.

The Conditions Due to Uncleanliness are due to obstruction of the excretory ducts, to accumulation of débris on the general surface of the skin, and to the consequent interference with the circulation.

1. The obstruction of the sudoriparous pores of the skin interferes with the elimination of waste products by the perspiration; these are re-absorbed or retained in the system; consequently more work is thrown on the lungs and kidneys, and the equilibrium of health is destroyed.

Sebaceous obstruction causes an accumulation of oily secretion in the ducts. The black spots so commonly seen about the nose, are the blocked up orifices of sebaceous glands, and by squeezing the nose tiny threads of fatty matter are forced out from the interior of these glands. Pimples on the face are usually due to obstruction of the sebaceous glands; sometimes the obstruction leads to inflammation around the sebaceous gland (acne) which often permanently injures the skin.

2. Accumulation of effete matter on the skin occurs, unless frequent ablutions are performed. The epidermis is constantly shedding its older and more superficial parts, in the form of minute scales or “scurf.” In the absence of frequent washing, the scales of epithelium tend to accumulate, the sebaceous secretion matting the scales together, and rendering them more adhesive. The saline matters of the perspiration also accumulate along with the scales and sebaceous secretion, and in virtue of their hygroscopic properties tend to keep the skin clammy and cold.

The obstruction of excretions and the accumulation of débris lead to other consequences. Thus:—3. The sensibility of the skin is dulled when the sensory papillæ are covered with dirt. The sensations received by the skin are important in regulating the temperature of the body. A cold external temperature should cause a reflex contraction of the small arteries bringing blood to the skin, thus diminishing the flow of blood and preventing undue loss of heat. Similarly, if the external temperature is high, or the internal development of heat is too great, these arteries dilate, and sending more blood to the skin, cause a greater loss of heat by radiation and conduction. Impaired sensibility of the skin leads to imperfect action of the reflex nervous mechanism to which the above effects are due, and consequently the dangers resulting from sudden alterations of temperature are greatly increased.

4. The tendency to chills is increased, not only by deficiency of the nervous tone of the skin, but also by obstruction of the pores of the skin, and by the hygrometric action of the saline matter collected on it.

5. Cutaneous diseases are due to, or favoured by, uncleanliness. These are of two kinds—parasitic and non-parasitic. Acne, which is the chief non-parasitic disease favoured by uncleanliness, has been already mentioned.

Parasitic skin diseases are greatly favoured by the presence of a dirty skin, which affords a suitable soil for the development of the parasites. (See also page [275]).

Uses of Soap.—Soap is produced by an action of an alkali on an oil. The alkali displaces glycerine from the oil, and forms an alkaline stearate, which is soap. Soft soap is chiefly stearate of potassium; hard soap is stearate of sodium. There may also be present the alkaline salts of oleic and palmitic acid. Soft soap is not used for washing the skin, as it is too irritating. All soaps contain a slight excess of soda; the greater this excess, the more irritating is the soap to delicate skins. Hard soaps may be also made with potash, if the fat employed be a solid one; but such soaps are rather softer than ordinary hard soaps, and more caustic. Cocoa-nut oil is used in making marine soaps, because, unlike all other kinds, it is not rendered insoluble by brine, and so will form a lather with sea-water. Normal soaps contain from 15 to 35 per cent. of water. “Liquoring” a soap consists in adding 5 to 25 per cent. of soluble silicates. By this means the soap may be made to hold 70 per cent. of water, which is obviously very wasteful.

In washing the skin, the water washes away a considerable amount of epidermis, and the saline matters which have collected. For the oily sebaceous secretion soap is required. The alkali in soap combines with the oily matter, forming an emulsion which carries away with it a quantity of the dirt which previously blocked the orifices of the sebaceous and sweat ducts. When the skin is rubbed by the towel after washing, the softened epithelium, and with it any remaining dirt, are rubbed off, leaving the skin clean, and able to perform its normal functions.

The Use of Baths.—The primary object of bathing is cleanliness. A secondary consideration is the pleasure derived from bathing. Baths are especially necessary for those persons who lead sedentary lives. When the skin is kept in an active condition by exercise, it to some extent cleanses itself. Thus, a farm labourer who has a weekly bath, may be really cleaner than a person of sedentary habits, who has two baths per week.

Baths are classified according to temperature as follows:—Below 70° Fahr. they are described as cold; tepid up to 85°; warm up to 97°; and hot over this temperature. It is important in deciding the temperature of a bath not to trust to one’s sensations; the only accurate measure is by the thermometer. A cold morning tub in the summer will commonly contain water at 55° to 60°; while the same in winter will be down to 40°, or occasionally to 32°.

For purposes of cleanliness the warm bath is the most efficient, combined with the free use of soap. The chief objection to it is that it produces an increased flow of blood to the skin, by relaxing the cutaneous blood-vessels, thus increasing the danger of chills if there is subsequent exposure. The increased sensibility to cold resulting from a warm bath may be obviated by afterwards rapidly sponging the body all over with cold water, and then drying the body quickly, and using the friction of a moderately rough towel. It is desirable for both cold and warm baths to have a “bath-sheet,” in which the person may be completely enclosed on coming out of the bath. Drying is thus much more quickly accomplished, and the danger of chill is minimised.

A daily morning cold bath is a most important agent in the maintenance of robust health. The first sensation on entering a cold bath is of shock, due to the cooling of the surface of the body. This is followed in a few seconds by a glow, due to the blood returning with considerable force to the skin. A cold bath ought to be taken as rapidly as possible. If soaping the body is desired, it should be done before entering the bath, and the stay in the latter should be little more than momentary. In this way the best reaction or “glow” is obtained.

If a feeling of cold and chilliness remains after a cold bath, it has done more harm than good. This condition may often be avoided by quick drying and brisk friction; if after this a good reaction is not obtained, the temperature of the water should be increased. For those who are not very robust, the “cold tub” in winter is to be deprecated. If the water be raised to 60° by the addition of warm water, or in some cases even to 70°, a good reaction may be obtained. In other cases, in which a reaction is not experienced even after a bath of the latter temperature, a tepid bath may be taken, and then the body rapidly sponged with colder water.

Cold baths increase the tone of the skin, rendering it less susceptible to changes of temperature. The tendency to “catch cold” is diminished, the blood-vessels and nerves of the skin both responding more readily to any stimuli.

Swimming is a valuable combination of bathing and exercise. A sudden plunge into cold water for swimming purposes is dangerous to those who are not hardened to it, and especially so in the case of running water, as in rivers or the sea. Here the water around the swimmer is constantly being changed, and each layer of water coming in contact with him abstracts a considerable amount of heat. Many of the cases of so-called death from “cramp” are really due to the benumbing and depressing influence of continued cold on the vital organs.

Swimming, under proper superintendence, ought to be universally enforced. The exercise accompanying it serves in most cases to counteract the depressing action of the cold water; but it is important in all cases to attend to certain rules. The immersion should not be prolonged; the body should be warm at the time of entering the water; and the bath should not be taken until about two hours after a meal; nor after prolonged fasting, as before breakfast.

Personal Cleanliness.—Personal cleanliness involves not only attention to the skin, which we have already considered, but to the hair, nails, mouth, and other parts of the body.

The hair ought to be carefully brushed and combed, but it is not desirable to use soap to it as often as to the skin. Soap removes the sebaceous secretion from the hairs, and renders them dry and brittle. Artificial pomades are, as a rule, unnecessary.

The nails should be cut square, and not down at the sides. It is hardly necessary to say that they should be kept clean: they may convey serious infection.

The mouth and all mucous orifices should be kept scrupulously clean. A fœtid breath is not uncommonly due to the discharges from carious teeth, or to the decomposition of food which has been allowed to accumulate in the cavities of teeth. Such decomposing matters when swallowed, are apt to produce indigestion; and this also occurs from imperfect mastication of food by the bad teeth. It is important that the teeth should be frequently cleansed, and that all carious teeth should be “stopped” at an early period, and tartar and other accumulations removed. Whether bad teeth, which are so extremely common, are due to the drinking of very hot liquids, or to the fact that the more perfect cooking of food gives less healthy friction to the teeth, is doubtful. Whatever the cause, by keeping the mouth thoroughly sweet and clean, and by having the carious teeth stopped as soon as discovered, their vitality may be greatly prolonged. Teeth should be periodically inspected by a competent dentist. Irregularities of the teeth may be corrected, if they receive early attention. Carious “milk-teeth” should receive attention from a dentist, as well as the permanent teeth.

General Cleanliness.—Next to cleanliness of the skin, that of the apparel is most important.

There is a general preference for colours “that do not show the dirt”; the fact that it is still there, though not seen, being partially ignored. Changing of apparel is commonly confined to underclothing. It is forgotten that vests, trousers, dresses, etc., acquire a large amount of dirt and organic matter, and ought to be changed and well aired at intervals.

Cleanliness in respect to bedclothes is very important. Organic matters evolved from the skin, lungs, etc., hang about the bed-linen, and give the bedroom the “close smell” which can be perceived on entering it in the morning straight from the fresh air. The beds should not be made directly after being evacuated, but the clothes should be thrown over the bottom of the bed, the bolsters and mattress well shaken, and every part exposed to a free current of air during the greater part of the morning, before re-arranging the clothes. Eider-down quilts, unless frequently ventilated by exposure to outside air, are unwholesome. Superfluous bedroom furniture should be avoided, as it all takes away from the breathing-space. Bed-hangings should be reduced to a minimum, and all excretory matters covered up during their stay in the room, and removed as early as possible.

Cleanliness of the house is also very important as a means of health. Dust, in however obscure a corner it rests, attracts to itself organic matters, and forms a soil in which disease germs may grow. Besides this, it devitalises the air, depriving it of its active oxygen. (See also page [101]).

Dust in the streets serves to carry about various diseases, besides mechanically irritating any part it comes in contact with, producing bronchitis, etc.

[CHAPTER XL.]
CLOTHING.

Physiological Considerations.—The average temperature of the surface of the body in man is 98·4 to 98·6°. The maintenance of a tolerably uniform temperature is an essential condition of life. The factors governing the temperature of the body are the amount of heat produced and the amount lost. If more heat escapes, more has to be generated; and the source of all the heat produced in the body is the food taken. This becomes changed by the metabolic processes occurring in the body which produce heat.

Heat is lost, (1) by the skin; (2) in respiration, the expired air having been heated during its stay in the lungs; (3) with the food and drink taken, if not at the temperature of the body; (4) with the excreta; and (5) by transformation of heat into mechanical energy. Of the whole loss by these different channels, probably eighty to ninety per cent. is through the skin.

The Loss of Heat by the Skin is in three different ways. First, by conduction, when the skin comes in contact with anything cooler than itself; secondly, by radiation into space; and thirdly, by evaporation of the perspiration. The last cause produces a considerable reduction of temperature, even when the perspiration is not so abundant as to be visible, but is in the form of insensible perspiration. The losses by these different sources vary in amount; when one is increased, another is diminished, by way of compensation. Thus, in very cold weather, the amount of radiation and conduction of heat are increased; but evaporation greatly decreases, and the diminished loss of heat in this respect counter-balances in some degree the increased loss by radiation and conduction.

When the external warmth is considerable, increased evaporation occurs; while when the weather is cold, the cutaneous arteries contract, and less blood goes to the skin, and so the loss of heat is diminished. In most climates, however, this action of the skin requires to be supplemented by some kind of clothing.

Requisites of Dress.—1. The first and most important requirement is that clothing should maintain a uniform and equable temperature in all parts of the body.

In hot climates clothes are required in order to protect the body from external heat. In this country, they are required to prevent the too rapid escape of heat from the body. For both these purposes, dress must be of a non-conducting material, in order not to encourage transfer of heat into or from the surrounding atmosphere.

The loss of heat by the skin may be prevented by interfering with radiation or conduction of heat, or with evaporation from its surface. Radiation of heat from the skin is prevented by clothing, the dress taking the place of the skin as a radiating surface. The amount of radiation from the dress will depend on the rapidity of conduction of heat from the skin. The amount of conduction and of radiation of heat will vary considerably with the material and colour of the dress.

As regards conductivity, the two extremes are represented by linen and fur. It is found that if the conducting power for heat of linen = 100, then that of wool = 50 to 70. This partly explains why woollen goods are so much warmer than linen. We shall find that there is another explanation in the relative hygroscopic properties of the two materials.

As regards radiation of heat, in one experiment it was found that while a piece of linen took 10½ minutes to cool, a corresponding piece of flannel took 11½ minutes.

Apart from the material, the colour of dress has some influence in regulating the loss of heat. Dark-coloured materials absorb more light and heat than lighter coloured materials; they may be good or bad conductors of heat, according to the nature of the material. White reflects the rays of light and heat; hence it is a poor absorber. In summer it prevents the passage of heat inwards, and, in winter, may prevent its passage from the body. It is thus well adapted for both winter and summer clothing, and has the additional advantage of being the cleanest colour.

Franklin placed a number of squares of different coloured cloths of the same material on snow, and found after a time that the snow covered by the black piece was most, and by the white piece least melted. In another set of experiments, shirting materials dyed various colours were taken, and it was found that if the rays of heat received by white were represented as 100, pale straw received 102, dark yellow 140, light green 155, Turkey red 165, dark green 168, light blue 198, black 208.

The influence of colour is antagonised to a large extent by the nature of the material; the increased heat absorbed by a dark material may be counterbalanced by the material being a good conductor. Also the influence of colour is only exerted superficially; hence, although it produces considerable effect in thin textures, as gauze, it has little influence on thick materials.

2. The dress should not interfere with perspiration. In order that it may not do this, it should be competent to absorb moisture easily, without its surface becoming wetted. Materials like linen which lose their porosity and rapidly become wetted by perspiration, cause rapid loss of heat from the body, inasmuch as water is a better conductor of heat than air. Pettenkofer found that while the maximum hygroscopic power of wool (flannel) is 174 and the minimum 111; the maximum of linen is 75 and the minimum 41. Hence, with a flannel vest next the skin, the liability to chill is much less than with a linen one. There is one slightly counterbalancing drawback; hygroscopic materials absorb moisture from the air, as well as from the skin. A woollen coat during a damp day, without rain, increases considerably in weight.

Waterproof clothing is injurious when worn beyond a short period, on account of its being non-porous and consequently keeping the body enveloped in a vapour bath composed of its own perspiration. For a similar reason India-rubber boots are objectionable, except for short periods; they make the feet damp, and even sodden. Sealskin jackets are objectionable for walking, not only because of their weight, but because they are not porous.

3. The warmth of clothing should be uniformly distributed throughout the body. This principle is very frequently departed from; and consequently one part may be chilled while another is over-heated. This is seen especially in female apparel. The same evil is seen in the short sleeves, and short and low-necked dresses of young children. “Combination” garments for women, and sleeves and leggings for young children are happily becoming more generally adopted, and will diminish the diseases due to exposure to cold.

4. The clothing should not be tight; and this for three reasons. First, because loose clothing is warmer than tight; this everyone has experienced in the case of gloves. The retention of air in the meshes of clothing is one of the main causes of its warmth, air being a bad conductor of heat. The imprisonment of air in the meshes of the material largely explains the warmth of eider-down quilts, furs, and flannels as contrasted with linen.

Secondly, clothing should not be tight, in order to avoid interference with the action of the muscles. Tight sleeves prevent the muscles of the arms and chest from being exercised. Tightly laced corsets imprison the trunk muscles, prevent their contractions, and so lead to muscular weakness and occasionally spinal curvature. Tight skirts similarly prevent free play of the lower limbs, leading to a halting gait, a diminished amount of exercise, with all the evils following deficient exercise. Tight clothing is not confined to one sex, and in all cases leads to hampered movements and deficient muscularity.

Thirdly, tight clothing tends to impede the functions of circulation, respiration, and digestion. The fashion which more than any other interferes with important functions is tight-lacing. This produces (1) compression and displacement of the viscera; the liver and the stomach especially suffer. (2) Respiration and circulation are impeded, the action of the diaphragm being impeded. (3) The muscles of the trunk being tightly encased, are incapable of movement, and consequently tend to waste and atrophy. The general outline of the body is altered. Instead of the waist being elliptical, as it naturally is, it becomes nearly circular; and instead of its circumference averaging twenty-six to twenty-seven inches, it may be eighteen to twenty-one inches. Tight garters tend to produce varicose veins.

Tight boots are injurious, as they tend to destroy the natural elasticity of the movements, and confine them within narrow limits. They act to some extent the part of splints. By interfering with the circulation of blood through the feet, they cause cold feet, and not uncommonly chilblains. High-heeled boots do not allow the natural elasticity of the foot to come into action. They distort the movements of the body and cause corns and bunions. Similar effects are produced by boots which are too narrow and have pointed toes, thus not allowing free movement of the toes.

5. The weight of the clothing should be the smallest amount consistent with warmth, and it should be evenly distributed. The chief weight should not be suspended from the waist, as here the parts are not well supported by bones. The shoulders and hips should share in the suspension of clothing, thus diminishing the danger of compression and displacement of internal organs. In order that garments may be as light as possible, they should be made to fit to each limb separately, thus diminishing the amount of material required.

6. The materials of dress should be as far as possible non-inflammable. This may sometimes be disregarded, but is often important, as in the nursery. In this respect, as in many others, wool possesses great advantages. Woollen fabrics smoulder rather than burst into flames, and thus the injury resulting from any accident is limited. Cotton is more inflammable than linen, linen than silk, and silk than wool. A closely woven cloth is less inflammable than one with open meshes.

Dress materials, and more particularly muslin, have been rendered non-inflammable by treating with a solution of ammonic phosphate, or ammonic phosphate and ammonic chloride mixed. The best material, however, is sodic tungstate, which, unlike the others, is not affected by ironing. Sodic molybdate is used in arsenals to render the workmen’s clothing non-inflammable. All the above plans are objectionable, as the weight of the material is increased 18 to 29 per cent., and they all wash out. To remedy this, a “fire-proof starch,” containing sodic tungstate has been devised.

Perfect non-inflammability is only required in certain dangerous occupations. The plans hitherto mentioned simply prevent the fabric breaking out into flame. The only cloth absolutely unaffected by fire is asbestos cloth.

7. Elegance of dress, although not so important as utility, is not to be neglected, and the two are perfectly compatible. In fact, elegance is indirectly associated with utility, for nothing which is awkward, or leads to obstructed movements or distortions of the body, is really elegant. A sudden constriction, as in a very tight waist, is not only bad from a hygienic point of view, but is also ugly.

Materials for Clothing.—The materials used are derived partly from the vegetable world, as hemp, flax, cotton; and partly from the animal world, as silk, wool, hair, feathers. The most important materials are wool, silk, cotton, and flax.

1. Wool varies somewhat in character, according to the animal from which it is derived. In all its varieties, however, it preserves the character of a bad conducting and porous substance, the two most important requisites in a dress material.

(1) Wool from the sheep is really a soft and elastic hair, composed of fibres three to eight inches long, and about 1 ∕ 1000 inch thick. The finer and shorter wools are used for fine cloth, the longer and coarser for “poplins,” “worsted pieces,” etc. Flannel is a woollen stuff of rather open and slight fabric. Wool is irritating to delicate skins, and may be so much so, that it cannot be worn next the skin, whether as flannel, worsted, or merino. In these cases, it may be worn outside a linen or gauze vest, and so all its advantages secured. It is one of the worst conductors of heat, and ought always to be worn in winter; while even in summer, it ensures a greater immunity from chill after perspiration than any other material.

(2) Cashmere is made from the down found about the roots of the hair of the Thibet goat. Imitation cashmere is made of various materials mixed together.

Fig. 56.
Microscopical Appearance of Fibres of
A—Cotton. B—Silk. C—Linen. D—Wool.

(3) Alpaca is obtained from the fleece of the llama, alpaca, and vicuna. It is longer than the fleece of the sheep, the fibres, which are soft and strong, averaging six inches in length. It is commonly made up with cotton or silk.

(4) Mohair is the hair of a goat inhabiting the mountains near Angora. It is woven into an almost waterproof cloth, and used in making plush, braid, etc.

2. Hair derived from the horse or cow differs from the hair usually called wool, in the greater solidity of its structure, which makes it ill adapted for clothing. Its chief use is in the manufacture of felts, of which hats are made.

3. Leather is a kind of natural felt, very close and firm in its texture. It is used in this country chiefly for boots, but in some colder climates also for coats, etc. It is impervious to moisture, like sealskin, and is consequently not very healthy. The same objection applies to chamois-leather underclothing, which is non-porous, and consequently keeps the skin hot and clammy; also, it cannot be washed without becoming stiff on drying. This necessitates wearing the material after it has become impregnated with perspiration.

4. Silk. The thread spun by the silk-worm is composed of filaments 1 ∕ 2000 inch wide, and is the strongest and most tenacious of textile fabrics. Its thread is three times as strong as a thread of flax of the same thickness, and twice as strong as a thread of hemp.

Its fibres are round like those of linen, but softer and smaller; it gives an agreeable sensation of freshness to the skin even more than linen. It is a worse conductor of heat than cotton or linen. Its great disadvantage for wearing next the skin, apart from its expense, is that it irritates delicate skins. Satin is silk so prepared as to form a smooth, polished surface.

Velvet is a silk fabric of which the pile is due to the insertion of short pieces of silk thread under the weft or cross-thread. Cheaper kinds are made, containing a certain proportion of cotton.

Crape is made of raw silk gummed and twisted to form a gauze-like fabric. Taffety, moire, brocade, and plush are made of silk alone or combined with cotton.

5. Cotton consists of the downy hairs investing the seeds of the gossypium plant. The threads of which it is composed are flat, ribbon-like, and twisted, about 1 ∕ 800 to 1 ∕ 2000 inch wide. Owing to its flat fibres with sharp edges, it is apt to irritate delicate skins; linen is preferable for dressing wounds for a similar reason. Cotton is warmer than linen, being a worse conductor of heat. It also absorbs moisture better, not becoming wet so soon; but it lacks the “freshness” which makes linen materials pleasant to wear. Calico, fustian, jean, velveteen, and muslin are the chief cotton fabrics.

6. Flax is formed from the fibres of the flax plant. Linen is made from it. Cambric and lawn are very fine and thin linen materials. The fibres of linen are round and pliable; thus it is smooth and soft, and peculiarly agreeable to the skin. It is, however, a good conductor of heat, and consequently “it feels cold” to the skin. Furthermore its pores quickly become filled with perspiration, which escapes rapidly, thus chilling the body.

7. Mackintoshes are valuable as a temporary protection against external wet. Worn for more than a short period, they produce great heat and a sense of closeness, owing to retention of the perspiration. The best form of mackintosh is one having a cape, with a space for evaporation between it and the rest of the garment.

The Amount of Clothing required varies with circumstances. 1. Health; those of robust constitution require less than the feeble. The more active are digestion and assimilation, the less is the amount of clothing required. If heat is preserved by clothing, less food is required. Thus a distinct saving of food is effected by warm clothes. Warm clothes are the equivalent of so much food that would have been required to keep up the temperature of the body, if the clothes had not been worn. Thinly clad persons under conditions of starvation die more quickly than those who are better protected.

2. Clothing requires to be adapted to climate and season. In winter and in cold climates the amount of clothing must be increased, and warmer materials chosen. In the changeable climate of Great Britain, it is difficult to adapt the character of one’s dress to the requirements of the weather. Clothing ought, however, not to be changed according to the calendar, but according to the weather. The tendency is to assume summer clothing too early in the spring, and to continue it too far into the autumn. According to Boërhave, winter clothing should be put off on Midsummer day, and resumed the day after. This, although rather exaggerated, may serve to impress the caution required. The same authority says that only fools and beggars suffer from cold, the latter not being able to procure sufficient clothes, the former not having the sense to wear them.

3. Age. Those at the two extremes of life are specially susceptible to cold. The mortality of infants during the first three months of life is nearly doubled in winter. Bronchitis and pneumonia prove fatal chiefly at the two extremes of age.

The younger a child the larger is its surface as compared with its bulk, inasmuch as the area of a body varies as the square of its dimensions, while its mass varies as their cube. Thus a cube 1 inch each side has 6 square inches of surface to 1 cubic inch of bulk, while a cube 10 inches each side has 600 square inches of surface to 1000 cubic inches in bulk. Similarly a child 1 ∕ 10 the size of its mother, besides its feebler powers of producing heat, has ten times as much surface in proportion to its size by which heat is lost.

After the age of thirty-five, it is better to exceed than to be deficient in clothing. A degree of cold that would act as a useful tonic to the robust and middle-aged, produces serious and even fatal depression of the vital powers in children or aged people. For the same reason it is advisable to discontinue cold baths as age advances.

A very pernicious delusion is prevalent, that children ought to be “hardened” to the influences of cold, and that too much clothing “makes them tender.” Excessive clothing may possibly increase the tendency to “catch cold,” owing to its exciting perspiration, or owing to the fact that the extra clothing is commonly thrown off at irregular intervals—witness the effects of wearing a scarf round the neck occasionally. But to suppose that children can be hardened by exposure of arms and legs, and other parts of their bodies, is irrational. A large amount of heat is lost from these bare surfaces, and apart altogether from the danger of chill, more food must be taken to compensate for this loss of heat, and keep up an equable temperature. Also if the food taken is expended in preserving the warmth of the unprotected body, less material is left for the purpose of growth. From these causes it frequently happens that children remain stunted in growth, even if latent disease is not actually developed by the extra strain on their resources.

The children of the very poor are often pointed to as demonstrating the power of hardening. It is forgotten how many of these poor children have perished under the hardening system, and that the good health of those remaining is in spite of the hardening.

Poisonous Dyes in Clothing.—These, like poisonous wall-papers, were formerly much more common than at present, and, as in wall-papers, the poisonous agent has most frequently been arsenic, large quantities of which were formerly used in the preparation of certain dyes. Occasionally such poisonous pigments are still employed.

The means of detecting arsenic in any fabric or wall-paper are given on page [216].

[CHAPTER XLI.]
PARASITES.

Parasites (Greek, para, upon, and siteo, I feed), in the broadest sense of the word, are living organisms, which derive their nourishment from other living organisms. They may belong to the vegetable or animal kingdoms, and may live on the skin, in the alimentary canal, or in some one of the internal organs. Some, like the fungus causing ringworm, feed on the living tissues of the animal infested; others, like tape-worms, on the partly digested food; while other parasites, like fleas, only pay temporary visits to the surface of the body, for the purpose of obtaining food.

Vegetable Parasites.—Vegetable parasites all belong to the class of fungi, and more accurately to the two lowest divisions of this class which have been provisionally formed, viz.—Schizophyta, and Zygophyta. The Schizophyta include two orders, Schizomycetes and Saccharomycetes.