Transcriber’s Notes

Obvious typographical errors have been silently corrected. Variations in hyphenation have been standardised but all other spelling and punctuation remains unchanged.

The original makes extensive use of „. This has been replaced by the original text in some cases where this improved clarity or layout.

The mathematical and chemical formulae accurately represent the original but have not been error checked.

HYGIENE:
A MANUAL
OF
Personal and Public Health

BY
ARTHUR NEWSHOLME, M.D., F.R.C.P., Lond.,
UNIVERSITY SCHOLAR IN MEDICINE; DIPLOMATE IN PUBLIC HEALTH, UNIV. LOND.; MEDICAL
OFFICER OF HEALTH OF BRIGHTON; MEMBER OF THE COUNCIL AND EXAMINER TO THE
SANITARY INSTITUTE; EXAMINER IN STATE MEDICINE TO THE UNIVERSITY OF
LONDON; LATE EXAMINER IN PREVENTIVE MEDICINE TO THE UNIVERSITY OF
OXFORD, AND PRESIDENT OF THE INCORPORATED SOCIETY OF MEDICAL
OFFICERS OF HEALTH.

NEW EDITION, 1902. ILLUSTRATED.

LONDON:
Geo. Gill & Sons, Ld., Minerva House, Warwick Lane.

[PREFACE.]

The writing of a preface is perhaps superfluous for a book which has had a large and steady sale for nearly twenty years, and which has evidently met with the approval of a large constituency. A few words of introduction appear, however, desirable in view of the facts that the present edition has been almost entirely re-written; that a large amount of new matter has been introduced; and that, so far as is known, the comments on each subject represent the most recent and authoritative knowledge upon it.

An attempt has been made to meet the requirements of medical students, as well as of science students and general readers, for whom former editions were chiefly intended. A large class of medical students and practitioners do not require the detailed statement of the subject contained in the larger text-books. For them, and, it is hoped, also for a large number of candidates for diplomas in public health and in sanitary science, the present edition will prove to be useful. At the same time, the subject has been treated as non-technically as is consistent with accuracy, in order to retain its suitability for non-medical readers. A large number of new illustrations have been introduced.

The new chapters dealing with Dietetics, Trade Nuisances, Meteorological Observations, Tuberculosis, Disinfection, and Vital Statistics will, it is believed, enhance the value of the book.

Attention is also drawn to the solutions of mathematical problems in the different branches of hygiene, of which a table of contents is given on page viii.

In its new form, it is hoped that this work will be found to have retained its value as a plain and straightforward account of its subject for the general public and for science students; and to have become a practical guide to sanitary inspectors and to medical students, whether preparing for a diploma in public health, or studying hygiene as an important branch of medicine. The use of smaller type for specially technical matter of less general interest will facilitate discriminative reading.

ARTHUR NEWSHOLME.

Brighton,
February 28th, 1902.

TABLE OF CONTENTS.

SPECIAL TABLE OF CONTENTS FOR ARITHMETICAL PROBLEMS IN HYGIENE.

HYGIENE.

[CHAPTER I.]
INTRODUCTORY.

In classical mythology, Æsculapius was worshipped as the god of Medicine, while his daughter Hygeia had homage done to her as the sweet and smiling goddess of Health. The temples of these two deities were always placed in close contiguity; and statues representing Hygeia were often placed in the temple of Æsculapius. In these statues she is represented as a beautiful maid, holding in her hand a bowl, from which a serpent is drinking—the serpent typifying the art of medicine, then merely an art, now establishing its right more and more to the dignity of a science.

That considerable attention was paid in very early times to matters relating to health, is also shewn by the elaborate directions contained in the Mosaic law as to extreme care in the choice of wholesome foods and drinks, in isolation of the sick, and attention to personal and public cleanliness. It is not surprising, therefore, to find that the Jews, throughout the whole of their history, have apparently enjoyed a high standard of health.

In this country great ignorance of the laws of Health has prior to the last fifty years prevailed, and consequently preventible diseases have been rampant, and have claimed innumerable victims. Each century has been marked by great epidemics, which have swept through the country, scattering disease and death in their course. In the fourteenth century, for instance, there was the Black Death, a disease so fatal that it left scarcely one-fourth part of the people alive; while Europe altogether is supposed to have lost about 40 millions of its inhabitants, and China alone 13 millions. A century and a half later came the Sweating Sickness (though there were a score of minor epidemics in between). This was carried by Henry the Seventh’s army throughout the country, and so great was the mortality, that “if half the population in any town escaped, it was thought great favour.” Considerable light is thrown on the rapid spread of this disease after its importation, when we remember that there were no means of ventilation in the houses; that the floors were covered with rushes which were constantly put on fresh without removing the old, thus concealing a mass of filth and exhaling a noisome vapour; while clothing was immoderately warm and seldom changed; baths were very seldom indulged in, and soap hardly used.

In the sixteenth and seventeenth centuries there were five or six epidemics of The Plague, and it was only eradicated from London, when all the houses from Temple Bar to the Tower were burned down in the Great Fire of September 2nd, 1666, which destroyed the insanitary and necessitated the building of new and larger houses.

Scurvy, jail-fever, and small-pox, are other diseases which were formerly frightfully prevalent. Jail-fever, the same disease as the modern typhus-fever, has now become practically extinct in its former habitat, owing largely to the noble work of John Howard, “whose life was finally brought to an end by the fever, against the ravages of which his life had been expended.” This disease was fostered by overcrowding, ill-ventilation, and filth.

Scurvy formerly produced a very great mortality, especially among sea-faring men. In Admiral Anson’s fleet in 1742, out of 961 men, 626 died in nine months, or nearly two out of every three, and this was no solitary case. Captain Cook, on the other hand, conducted an expedition round the world, consisting of 118 men; and although absent over three years, only lost one life. He was practically the first to demonstrate the potency of fresh vegetables in preventing scurvy.

The striking facts respecting small-pox will be found on page 293. The general death-rate has also greatly declined. Thus while the annual death-rate in London 200 years ago was 80 per 1,000, it only averaged 18.8 in the four years 1896-99; and the death-rate of England and Wales has declined from 22.4 in 1841-50 to 18.7 per 1,000 in 1891-95 and 17.6 in 1896-99.

That much still remains to be done is evident on every hand. There is little doubt that the general death-rate might be reduced to 15 per 1,000 per annum, instead of the present 18, were the laws of health applied in every household and community. It has been estimated that on the average at least 20 cases of sickness occur for every death; therefore nearly half of the population is ill at least once a year. A simple calculation will show how much loss the community annually suffers from this vast mass of preventible sickness. It amounts to many millions of pounds, leaving out of the reckoning the suffering and distress which are always associated with sickness. For details relating to special diseases, see page [297].

In the prevention of this mass of sickness, the knowledge of its causation is half the battle; when once a disease is traced to its source, as a rule, the agency which produces it can be avoided.

The reason why even more progress has not been made in the prevention of disease is not far to seek. In order to prevent a disease it is necessary to remove its causes. The causes of disease can only be ascertained by a careful investigation of its phenomena; and it is only within the last century that these have been studied to any large extent scientifically. Such knowledge of morbid processes not only results in improved measures of treatment, but in more rational and complete measures of prevention. Thus, not only is the number of diseases which are curable becoming gradually augmented, but the number preventible is even more rapidly on the increase.

Inasmuch as the preservation of health involves the prevention of disease, Hygiene, the science of health, is sometimes called Preventive Medicine.

The subject of Hygiene naturally divides itself into two parts, the health of the individual, and that of the community, or Personal and Public Health.

The former treats of the influence of habits, cleanliness, exercise, clothing, and food on health; while the latter is concerned with the interests of the community at large, as affected by a pure supply of air and water, the removal of all excreta, the condition of the soil, and with the administrative measures required to secure the removal of evil conditions. It is obvious, however, that these two divisions are not mutually exclusive. What is important to the health of the community, is equally so to each individual member of it. The purity of air and water, for instance, is of immense importance both personally and collectively.

It will be convenient to study first the three main factors in relation to health—food, water, and air—subsequently considering other matters of importance to health (see pages 4-157).

[CHAPTER II.]
FOOD.

Physiological Considerations.—All substances are foods which, after undergoing preparatory changes in the digestive organs (rendering them capable of absorption into the circulation), serve to renew the organs of the body, and maintain their functions. Foods have been classified as tissue producers or energy producers, the first class renewing the composition of the organs of the body, and the second class supplying the combustible material, the oxidation (or more correctly the metabolism) of which is the source of the energy manifested in the body. The two main manifestations of energy in the body are heat and mechanical motion, which are to a large extent interchangeable.

All foods come under one of these heads; they are either tissue or energy producers. They may be both, and in many cases are so. Thus, all nitrogenous foods (as meat, legumens, etc.) not only help to form the nitrogenous tissues of the body, but their largest share becomes split up into fats and urea, and so forms a source of heat to the body. Similarly fats may possibly, after assimilation, enter into the composition of the various tissues containing fat (of which the brain is the most important), though they usually supply an immediate source of heat. Proteid foods are, however, the tissue producers par excellence, other foods serving as the immediate sources of energy when metabolised in the body.

Certain foods do not directly serve either as tissue or energy producers, but are useful in aiding the assimilation of food. Such are the various condiments which may be classed as adjuncts to food. Salt is so necessary to the assimilation of food and to the composition of the various tissues, that it may be ranked as an important food. Water, again, though already oxidised, and so not an immediate source of energy, is absolutely necessary to the assimilation of food, to the interchange between the various tissues and the blood, and to the elimination of effete products.

Classification of Foods.—Inasmuch as milk supplies all the food necessary for health and growth during the first year of life, it may reasonably be expected to afford some guidance as to the necessary constituents of a diet for the adult; although the conditions of life being altered in the latter, we can hardly expect the same proportions of the different materials to hold good. In the infant rapid growth and building up of new tissues and organs are going on, involving the necessity for a larger proportional amount of nitrogenous food than in the adult.

The following is the average composition of 100 parts of

It is evident from this analysis of milk that our food must contain (at least) representatives of all the above divisions. We have, therefore:—

• 1. Nitrogenous Foods.
• 2. Hydrocarbons or Fats.
• 3. Carbohydrates or Amyloids.
• 4. Salts.
• 5. Water.

Condiments and stimulants (tea, coffee, alcohol) are not foods in the strict sense of the word, and will be discussed in a later chapter.

Nitrogenous Foods include albumin, casein, gluten, legumen, fibrin, and gelatin. They all agree in consisting of a complex molecule containing many atoms of carbon, hydrogen, oxygen, and nitrogen, with the addition of smaller quantities of sulphur, and in some cases phosphorus. The nitrogenous substances used as food may be divided into two groups, (a) those containing gelatin, and (b) numerous bodies which receive the common name of proteids or albuminoids.

The percentage composition of gelatin is:—

The percentage composition of all proteids lies within the following limits:—

Proteids also contain a small amount of phosphorus, chiefly as phosphate of lime, but also in minute quantity in their essential structure. Various proteids are used in food, e.g. serum-albumin in the blood and tissues of animals; egg-albumin in the white of eggs; myosin in flesh; casein in milk; legumin, or plant-casein, in the seeds of leguminous plants; gluten in wheat-flour, etc.

Proteid foods are pre-eminently important, as they construct and keep in repair the tissues of the body. They are not used solely for this purpose. A large share of the energy of the body is derived from the metabolism of proteids. The amount required for these purposes will be discussed on page [32]. Meanwhile, it may be said that it is not found to be compatible with efficient health simply to supply an amount of proteid food which will suffice to replace the wear and tear of the tissues, leaving fats and carbohydrates to supply the energy of the body. Deficiency of proteid food always leads to ill-health; and it would appear that in all cases proteid food determines, to a large extent, the metabolism of non-nitrogenous food, and so is favourable to all vital action. The action of nitrogenous food in thus increasing metabolism may make it, when in relative excess, a tissue waster. Banting’s cure for corpulence is founded on this principle, lean meat alone being taken, all starchy and saccharine foods being carefully avoided.

By metabolism is meant the changes undergone by food before it reaches the state in which it is finally eliminated from the body. It is commonly spoken of as oxidation, but this word less exactly represents the facts. The complexity of the changes undergone by food in the body may be better appreciated by a glance at the following schematic statement, which only gives an approximation to the truth:-

Hydrocarbons, or fats, consist of three elements, carbon, hydrogen, and oxygen, the amount of oxygen present not being sufficient to oxidise completely either the hydrogen or the carbon. Thus the molecule of stearin, which may be taken as a typical fat, has the formula C₃H₅ (C₁₈H₃₅O₂)₈.

In respect to their comparatively unoxidised condition fats compare favourably with starch and sugar, C₆H₁₀O₅ and C₆H₁₂O₆ respectively. It is evident that in starch the H₁₀O₅ = 5H₂O, and that in sugar H₁₂O₆ = 6H₂O, so that in both cases only carbon remains uncombined with oxygen. Dried fats produce by their oxidation 2¼ times as much heat as a corresponding amount of sugar or starch; but the relative advantage of fat is not quite so great as would appear from this comparison, inasmuch as metabolism within the body is not identical with oxidation.

The fat obtained from food is not simply deposited in the body as such, to form a store of combustible matter, and to fill up the interstices between the different tissues. If this were so, the kind of fat deposited would vary with the food, which is not the case. The fat of the body is probably not formed directly from fatty food, but as the result of the metabolism of nitrogenous foods when this metabolism is incomplete. In the formation of milk this can be distinctly proved: the fat cells are formed from the protoplasm of the cells of the mammary gland.

Possibly carbohydrate food may be a source of fat, as well as nitrogenous and fatty food. This appears to be the case in the Strasburg goose, which is kept penned up in a warm room, and fed entirely on barley-meal, in order to produce an enormous fatty liver for the delicacy termed pâté de foie gras. But it may be that the large accumulation of fat in the liver is due to the warmth and inaction of the goose diminishing metabolism, and producing a fatty degeneration of the nitrogenous material of the liver.

Fats and carbohydrates, unlike proteids, do not excite metabolism in the system, and so, if in excess of the requirements of the system, can be stored up with comparative ease. Quiet and warmth, diminishing metabolism, conduce to the accumulation of fat in animals being fed for the market; and the same applies to human beings.

Carbohydrates or amyloids include the various starchy and saccharine foods. They are inferior to fats in nutritive power, but, being very digestible, are in much greater favour. In the process of digestion, starch is converted into grape sugar, and starch and sugar are practically equal in nutritive power.

Even when carbohydrates are entirely absent from the food, they may be produced in the organism by the breaking up of nitrogenous matter. This certainly happens in diabetes, in which the nitrogenous food rapidly becomes converted into sugar and urea.

The deprivation of carbohydrate food is much better borne than that of fats, because in the latter the hydrogen is not completely oxidized, and because fats aid the assimilation of other food.

Salts, and especially common salt (chloride of sodium), are essential to health. An average adult human body contains about seven pounds of mineral matter, of which about five-sixths is in the bones. On analysis the whole body yields about five per cent. of ash.

Chloride of sodium is necessary for the production of the acid (hydrochloric) of gastric juice, and of the salts of bile; half the weight of the ash of blood consists of it. An adult requires 150 to 200 grains of salt per day; a large part of this is taken in meat, bread, etc.; and but little need be taken as a condiment. Potassium salts form an important part of milk, muscle juice, and the blood corpuscles. They are obtained from bread and fresh vegetables and fruits. It has been maintained that deficiency of potassium salts causes scurvy (see page [28]); but this is now discredited, and probably potash is chiefly useful because of the vegetable acids with which it is associated in fruits and vegetables, which when oxidised, help to maintain the alkalinity of the blood, e.g., tartrates, citrates, and malates, which become carbonates in the circulation. Calcium phosphate (bone earth) is essential for the growth of bones, and is very important for the young. The best source for it is milk. There is more lime in a pint of milk than in a pint of lime water. Next to milk, come eggs, and then cereals, especially rice as a source of calcium. Lime salts and phosphates as drugs do not benefit like the same substances taken in natural food, and rickets is not curable by taking such drugs.

Oxide of iron is always present in the ash of blood and muscles, and in smaller quantities in milk. Fish and veal are usually deficient in it, while beef and yolk of egg are foods richest in iron. The amount of iron required in food is minute, and it is amply supplied by ordinary diet.

Phosphorus is an essential building material for the body. It is contained in foods chiefly in organic combination. The foods richest in it are yolk of egg, sweetbread (thymus), fish-roe, calves’ brains, and the germ of wheat. Milk and cheese are very rich in phosphates.

Water forms an important article of diet. This is evident from the fact that 80 per cent. of the blood consists of it, and 75 per cent. of the solid tissues; and from the fact that the daily loss of water from the system averages 50 ounces (2½ pints) by the kidneys, and about 40 ounces by the skin and lungs. Water is not simply received into the system as a liquid. It forms a large proportion of the solid food taken. Thus, 87 per cent. of milk, 78 per cent. of fish, 72 per cent. of lean meat, 38 per cent. of bread, 13 per cent. of peas, and 92 per cent. of cabbage, consist of water.

Solid food is dissolved in the alimentary canal by the watery secretions derived from the blood. Water swallowed as food, begins to pass on into the intestine at once. The statement that free consumption of water at meals delays digestion by diluting the gastric juice is therefore not well grounded. In the blood, water serves to carry nutrient materials to all the tissues; and, at the same time being circulated all over the system, equalises the temperature, favours chemical changes, and washes all the tissues. By water again, the effete matters which have been separated by the kidneys are washed out of its tubes.

The Oxygen of the air, in a broad sense, forms one of the foods of the system. This will be considered later.

Besides the above classification, foods have also been classified as follows:—

1. Inorganic food—Oxygen, salts.
2. Organic foods		Animal		Nitrogenous.
				Non-nitrogenous.
		Vegetable		Nitrogenous.
				Non-nitrogenous.
Or, as—
1. Solid foods		Animal		Nitrogenous.
				Non-nitrogenous.
		Vegetable		Nitrogenous.
				Non-nitrogenous.
2. Liquid foods		Water.
		Milk and its products.
		Tea and similar beverages.
		Alcoholic beverages.
3. Gaseous foods—Air.

[CHAPTER III.]
THE VARIETIES OF FOOD.

Nitrogenous Animal Foods.—These are divided into two groups, the one containing gelatin, and the other all the proteid or albuminoid substances, which are taken in the flesh of various animals, and in milk and eggs.

Gelatin is obtainable from bones, and from connective tissue wherever found. Being easily digested, and absorbed, it has been very popular as an invalid’s food; but the fact that animals cannot sustain life on it without the addition of proteids proves that its value is limited. It is incapable of building tissues, but is a valuable proteid-saver, being able to save from metabolism half its weight of proteid, or twice as much as is spared by an equal weight of carbohydrate. Its utility in this direction is, however, limited, because of the dilute form in which it is taken in ordinary foods. It is useful for invalids, partly because it forms a bulk, and prevents the evil tendency to give their food in too concentrated a form; partly because it forms a source of easily metabolised material, and so prevents tissue-waste; and partly because it commonly contains phosphate of lime, derived from the bones forming the source of gelatin.

Gelatin as prepared for the table contains a considerable proportion of water; as little as one per cent. of gelatin in water will cause it to gelatinise on cooling. Isinglass obtained from the floating bladder of the sturgeon is an example of the purest kind of gelatin; glue is an inferior sort, made from bones, etc.

Gelatin is only a cheap food when obtained, for instance, from bones which cannot otherwise be utilised. When made from veal it is costly out of proportion to its dietetic value.

The Flesh of various animals is one of the main sources of our nitrogenous and fatty food. Meats may be divided into two kinds, viz., red meat and white meat. These gradually merge into one another. As common examples of red meats, we have beef, mutton, pork, game, wild fowl, and salmon.

The common fowl and turkey, most fishes, rabbits, crustaceans, and molluscs, are examples of white meat. As a rule white meats are more digestible than red, having more delicate fibres, and containing a smaller proportion of nitrogenous matter.

Flesh consists almost entirely of muscular tissue, of which there are two kinds, striped and unstriped.

The striped is the variety most commonly used as food. Unstriped muscle has a softer texture, but is not so easily masticated as striped, and for this reason may be indigestible. Tripe is composed of the unstriped muscle and connective tissue of the stomach of the cow, and if well cooked forms a cheap and easily digested dish.

The influence of feeding on the quality of the meat is great. In ill-fed or old animals, connective tissue is more abundant, and the meat is tougher. Well-fed and fattened meat contains for equal weights much more nutritious matter than non-fattened meat, the fat which is deposited in the muscle replacing water and not proteid. Hence the gain in nutritive value is an absolute one, and is not attained at the expense of the proteid part of the meat. Young animals, again, contain more water and fat and a larger proportion of connective tissue than the full-grown, and are consequently not so nourishing.

Meat ought to be eaten either before the onset of rigor mortis, or near its end, before putrefaction has commenced. During rigor mortis it is denser, tougher, and more difficult to digest than after it.

The proportion of fat in meat varies greatly in different individuals of the same species, in different animals, and in different parts of the same animal. According to Dr. Ed. Smith, the proportion of fat in fat oxen is ⅓, in fat sheep ½, in calves ⅙, lambs ⅓, and fat pigs ½.

Good meat, whether beef or mutton, ought to have a marbled appearance, a medium colour, neither pale pink nor deep purple; its texture should be firm, and not leave the impress of the finger; its odour slight and pleasant, the juice reddish and acid, the bundles of fibres not coarse, and free from foreign particles imbedded in them; and lastly, it should not be taken from an animal killed near the time of parturition, nor in consequence of any accident or disease.

Beef is, as a rule, more lean than mutton or pork; it has a closer texture, and more nutritive material in a given bulk. It is also fullest of the red-blood juices, and possesses a richer flavour than the two others.

Liebig’s beef extract contains little if any albumin or gelatin. It is a useful stimulant to the gastric secretion, as in soups at the beginning of a meal, but is not a food. Its chief constituents are the various extractives of meat, the most important of which are inosinic acid, kreatin (C₄H₉N₃O₂,H₂O), and inosite, or muscle sugar (C₆H₁₂O₆, 2H₂O). Even in substances like Bovril, containing powdered meat fibre mixed with Liebig’s extract, the amount of nutritive material is very small. The white of one egg contains as much nutritive matter as three teaspoonsful of bovril. None of these substances can be trusted like eggs or milk to keep a patient alive for several weeks.

Mutton is regarded as being more suitable for people of sedentary occupation than beef. Lamb is more watery than mutton, and less nutritious.

Veal, as ordinarily prepared in this country, is difficult of digestion; its shreddy, juiceless fibres eluding the teeth, and consequently not undergoing proper mastication.

Pork is not so digestible as beef or mutton, partly because of the large proportion of fat, and partly because its fibres are hard and difficult to masticate. Its digestibility varies greatly with its age, breeding, and proportion of fat.

The Flesh of Birds contains very little fat, and that found separate from the meat is rarely nice. Most birds are edible, but fish-eating birds are apt to be nasty. As a rule, the flavour of the male bird is richer than that of the female. The chief virtues in poultry are their tenderness, and the large proportion of phosphates they contain. They are deficient in fat and in iron. To compensate for the former, one commonly takes with them melted butter and fat bacon or pork sausages; to compensate for the latter, the addition of Liebig’s extract to the gravy is useful. Young, and consequently tender, birds are known by their large feet and leg-joints. When a bird appears at table with violet-tinged thighs and a thin neck, if possible avoid being helped to the leg. Wild fowls are harder and less digestible than tame. In ducks and geese fat is more abundant, and of a stronger flavour; they are, consequently, not so digestible as fowls.

Fish forms an important article of diet. It is easily cooked, and usually very digestible; it possesses a larger bulk in proportion to its nutritive quality, and hence is very valuable for those who habitually take an excess of meat food, which is commonly the case with those leading sedentary lives, and in declining years. There appears to be no foundation for the statement that fish is rich in phosphorus, and is thus a good brain food. Generally, white-fleshed fish is more digestible than red-fleshed (such as salmon), the latter usually containing more fat than the former. When the fat is distributed throughout the flesh, as in the salmon, fish is more satisfying than when it is mainly stored up in the liver, as in the cod-fish. According to Payen, the percentage proportion of fat in soles is only 0.248, in whiting 0.383, conger eel 5.021, mackerel 5.758, eels 23.861. The addition of some fatty food, as melted butter, is very advisable to such meats as poultry, rabbits, soles, whiting, plaice, haddock, cod, turbot, and other fishes; whereas sprats, eels,. herrings, pilchards, salmon, etc., are more or less rich in fat.

A Hen’s Egg usually weighs a little under two ounces. It consists of 74 per cent. of water and 26 per cent. of solid matter. The white of the egg is chiefly albumin, the yolk consists of a very digestible oil, rich in phosphorus and iron, each particle of the oil being enveloped in a form of albumin called vitellin. The salts are chiefly contained in the shell. There is no sugar in the egg, the necessity for such oxidisable material for the chick being obviated by the heat produced by incubation. Eggs, when kept for some time, lose weight, owing to evaporation through the porous shell; similarly, air entering from without sets up decomposition. In a solution of brine containing an ounce of common salt to half a pint of water, fresh eggs sink, stale ones float; rotten eggs may even float in fresh water. Eggs may be preserved by keeping them in brine, or, better still in lime water, or by smearing them over with lard or butter, as soon as possible after they are laid.

Cow’s Milk has a specific gravity of 1028-34, and on allowing it to stand in a long narrow vessel ought to form ten or twelve per cent. of its volume of cream. The percentage composition of human and cow’s milk has been given on page [5]. The legal minimum standard for dairy milk, which is presumably derived from a number of cows, is now 3 per cent. of fat, and 8.5 per cent. of “solids not fat.” This standard is unfortunately very low, and allows a considerable margin of adulteration, which cannot be prevented by legal means. Thus ordinary milk derived from a herd of cows would probably contain 4.5 per cent. of fat; and it is, therefore, practicable to mix pure new milk with a large proportion of separated milk, and yet keep within the legal standard. This is largely done in towns, and infants suffer much from the deficiency of cream in their sole food (see page [28]). The lactometer determines the specific gravity, which should be taken at a temperature of 60° F. In skimmed or separated milk it will be over 1034; watering on the contrary lowers the specific gravity. If the milk has been both watered and skimmed the specific gravity will give an uncertain indication. Measurement of the cream in a tall narrow glass will enable one to detect the second possible source of fallacy; but the composition of milk can only be certainly determined by analysis. This is done (a) by evaporating a weighed amount of milk to dryness and then re-weighing. (b) From a separate amount of dried milk the fat is extracted by ether, the ether then evaporated, the remaining fat weighed, and its percentage calculated. The weight of fat deducted from the total solids i.e. (b) from (a), gives the “solids not fat.” The following example will make the method then followed clear. The sample gives 7.9 per cent. of “solids not fat.” Genuine milk contains at least 8.5 per cent. of “solids not fat.”

Then the sample contains—

100 × 7.9 ∕ 8.5 = 92.9 per cent. of genuine milk,
i.e. 7.1 per cent. of water has been added to it.

Half a pint of milk supplies as much nitrogenous nutriment as two good-sized eggs, and as three and a half ounces of beef. Milk may be deteriorated (1) by skimming or “separating” by machinery, or (2) by the addition of water—the first diminishing the proportion of fats, and the second the total amount of solids.

Skim Milk still contains nearly 1 per cent. of fat, but Separated Milk, in which the cream has been removed by centrifugal apparatus, contains less than ¹ ∕ ₈ per cent.

Skim or separated milk forms a cheap source of nitrogenous food; but when it is sold mixed with new or alone as new milk, the public is defrauded, and infants fed on it are robbed of the fat which is so essential for their growth.

Condensed Milk is milk deprived of a large part of its water. It represents three times its volume of fresh milk. There are in the market (a) unsweetened and condensed whole milk, (b) sweetened and condensed whole milk, and (c) sweetened and condensed skim or separated milk. Unfortunately the latter is most largely sold because cheapest; and infants are thus often robbed of fat, a most important element in their food. Always examine the label of each tin carefully, to ascertain whether the milk has been deprived of its cream. The law requires that this fact should be stated on the label. Tins which have bulged should be rejected. Condensed milk is more easily digested by infants than new cow’s milk, but it lacks the anti-scorbutic properties of new milk (see page 28). Even the condensed whole milk if diluted beyond 1 part of milk to 3 of water is deficient in fat. Sweetened condensed milk has one-third its weight of extraneous sugar added to it, and on this account it tends in children to produce fatness, and a distaste for simple food; in children fed on it alone ossification (formation of bone) is retarded, and resistance to illness is diminished. The only dietetic advantages it possesses over fresh cow’s milk are its freedom from possible disease germs and easier digestibility.

The digestion of milk is preceded by its clotting in the stomach. The same thing happens when junket is formed by the addition of rennet to milk. This is a different process from the curdling of milk, which occurs when milk turns sour. The latter is caused by the splitting up of milk sugar and the formation of lactic acid by certain micro-organisms in the milk. When milk is heated, a skin is formed, consisting of coagulated albumin, in which is also a little casein, fat, and salts of lime. Boiled milk becomes sterilized. Cow’s milk should always be boiled, unless it is quite certain that the cows from which it is derived are perfectly healthy, and that the milk has not been exposed to infection before reaching the house. The disadvantages of boiling which are outweighed by its advantages, are that the taste of the milk is altered, some nutritive matter is lost by the formation of the “skin,” and the casein is not quite so easily digested. Pasteurization of milk, i.e. keeping it at a temperature of 70° C. (158° F.) for 20 to 30 minutes has been proposed as an alternative to boiling. This appears to destroy the bacilli causing tuberculosis (see page [312]). The typhoid bacilli are killed at 60° C. in five minutes when suspended in emulsion. Pasteurization is not, however, so certainly efficacious for other disease-germs as is boiling, and is not so easily carried out in domestic life as boiling. By boiling milk in a double saucepan, i.e. in a water-bath, very little change occurs in the taste of the milk, especially if it be cooled rapidly and strained.

Cheese is prepared by coagulating milk by “rennet,” the mucous membrane of the fourth stomach of the calf, salted and dried before using. By this means the casein is precipitated, carrying down with it the cream, and a large proportion of the salts of milk. The whey, containing the sugar, soluble albumin, and remaining salts, is separated by straining, while the mixed curd and fat are pressed in moulds. Cheese thus consists of casein, fat in varying proportions, water and salts, especially phosphate of lime. It is coloured with annatto, a vegetable colouring matter. When new, cheese is tough; when old, its oils tend to become rancid; the best age is from nine to twenty months. It is probable that cheese in small amount helps the digestion of other foods, though it is itself a highly concentrated and comparatively indigestible food. When toasted it is proverbially indigestible.

There are many different kinds of cheese. The following classification gives the more important varieties:—

(1) Cream cheese is the new curd only slightly pressed, and is more digestible than ordinary cheese.

(2) Next to these are cheeses made with whole milk rich in cream, such as Stilton, Gorgonzola, Cheshire, and Cheddar.

(3) Cheeses made of poor or partially skimmed milk, such as Shropshire, Single Gloucester, and Gruyère.

(4) Cheeses made of skimmed milk, such as Suffolk, Parmesan, and Dutch.

American cheeses may belong to any of these classes; they are generally pure, but occasionally are made from separated milk, margarine being added to take the place of cream. The sale of such cheeses, except under the name of “margarine cheese,” is now illegal.

Non-Nitrogenous Animal Foods.—These are all fats, and the most important are the various meat fats and butter. They possess a higher food value than carbohydrates in the proportion of 2¼; to 1. The composition of the various fats differs somewhat; they usually contain varying proportions of olein, palmitin, and stearin, which are compounds of glycerine with the radicle of a fatty acid (stearin = C₃H₅ (C₁₈H₃₅O₂)₃). Thus mutton suet consists of stearin, olein, and palmitin, with a preponderance of stearin. Beef suet contains less stearin and more olein than mutton suet. The more olein a fat contains the less solid it is. Olive oil is composed almost entirely of olein. Palmitin, which melts sooner than stearin, is the chief solid constituent of butter, while olein is its chief liquid constituent. Butter is specially distinguished by containing 7 to 8 per cent. of “volatile fatty acids,” such as butyric, caproic, etc., combined with glycerine. The presence and amount of these compounds is an important test for the freedom of butter from adulterating fats.

Cod-liver oil is next to butter the most digestible animal fat known. The best cod-liver oil is frozen at a low temperature, by which means the stearin is frozen out, and nearly pure olein is left. Traces of iodine have been found in it, and more commonly a small amount of bile, which probably increases its digestibility.

The temperature at which a fat becomes hard is a fair guide to its digestibility. Thus we know that beef, and still more, mutton fat, would become solid, under conditions in which bacon dripping is still soft. Where digestion is weak, there may be an instinctive loathing of fat meat; for such persons, especially for children, some other fat should always be substituted. Thus the addition of butter to the potatoes makes up the deficiency.

Butter forms 3½ to 4½ per cent. of cow’s milk. It is separated from milk by churning, the oil particles being deprived by this means of their albuminous coats. The more completely the butter-milk is separated the longer the butter keeps. It can be kept longer if salt is added, or in hot weather by keeping it under frequently-changed water. Rancidity indicates the decomposition of traces of the fat of butter into its fatty acid and glycerine.

Cream contains about 30 per cent. of butter fat, Cheshire cheese 25 per cent., and skim milk cheese 7 per cent.

Butter milk differs from skim milk in the presence of lactic acid. It is more digestible than skim milk, the casein being in a more flocculent condition.

The odour and flavour of butter are not due to olein and palmitin, the two chief constituents, but to a smaller quantity of butyrin, caproin, and caprylin fats of a much lower series. Ordinary butter contains a considerable proportion of water, and the presence of about 8 per cent. renders it more palatable; if it is over 15 per cent., the butter is considered adulterated. An excessive amount of salt is sometimes present. The most frequent adulteration is the substitution of foreign fats for butter fat, e.g. lard, palm oil, rape seed oil, or cocoa-nut oil. Margarine is most frequently used for this purpose.

Margarine is prepared from beef-fat by melting, the stearin becoming solid again at a temperature at which olein and margarine still remain liquid. It forms a wholesome and cheap food, being nearly as digestible as butter, for which more expensive food it is often fraudulently sold. When mixed with a small proportion of butter its recognition by smell, etc., is almost impossible, but on careful chemical analysis, it is found to have a higher melting point and a lower specific gravity than butter, and a much smaller percentage of soluble fatty acids than the latter. Thus:—

Cereal Foods.—Gluten is peculiar to plants, and is chiefly found in plants belonging to the great family of grasses. Gluten is to bread what casein is to milk, and myosin to flesh. If one takes a piece of dough made from wheat flour, and holds it under a stream of water from the tap, a large part of it is washed away, while a sticky adherent mass is left behind. This is gluten, and it is its tenacity which enables bread to be made. If the fluid with which the dough was washed is collected, it will be found to contain a large quantity of starch, a small amount of sugar, of albumin, and certain salts. All cereals possess these constituents in various proportions, as may be seen from the following table:—

The proteid varies in character in the different cereals; wheat flour has the largest proportion of gluten (8 to 12 per cent.) and therefore makes the best bread.

Good wheat flour ought to be white, not gritty or lumpy, not acid or musty, forming a coherent stringy dough. Examined microscopically, it should show the absence of any fungi, or acarus farinæ, or of foreign starches, such as barley, maize, rice, potato, known by the different shape of their starch granules. (See Fig. 1.) Alum has been occasionally added to flour, to enable the baker to make a white and porous bread from damaged wheat flour. It can be detected as follows:—Pour over the freshly cut surface of a slice of bread some freshly prepared decoction of logwood chips, and then a solution of carbonate of ammonia. If alum is present, the bread turns a marked blue to violet colour; but if the bread is pure, it is only stained pink.

The wheat grain may be used as food in its entirety. Thus boiled in milk, after having been soaked in water, it forms the chief constituent of frumenty. Usually it is converted into flour by grinding or milling. A grain of wheat consists of three parts, an outer envelope, the bran, consisting chiefly of indigestible cellulose, and composing 13½ per cent. of the grain; the kernel, or endosperm, which makes up 85 per cent. of the grain; and the germ, forming 1½ per cent. of the grain. In the old method of stone grinding, the bran was removed, and the germ left along with the endosperm. In the elaborate processes of modern roller milling, the bran is removed as in the old grinding, because it cannot without the greatest difficulty be reduced to powder; and the germ is also removed, because the oil abundantly present in it is apt to become rancid and spoil the flour, and because the soluble proteids in it are apt to change some of the flour into dextrin and sugar, which become brown in baking and spoil the appearance of the bread. The germ is easily removed, because its toughness causes it to be flattened out in the milling, while the endosperm becomes powdery. The central part of the endosperm is the source of ‘patents.’ It is very rich in starch and is used for making fancy breads and pastry. The outer part of the endosperm is ‘households.’ ‘Households flour’ is subdivided into (a) second patents, or ‘whites’; (b) first households; (c) second households or ‘seconds.’ ‘Seconds’ is richest in gluten, ‘whites’ in starch. Ordinary bread is normally derived from a blend of these three. Some ‘strong’ wheats, e.g. Australian, yield a ‘patents’ which is rich in gluten, and such flour is used for making Vienna bread. ‘Strong’ wheats take up most water in baking, and so yield most loaves per sack. ‘Seconds’ flour yields a bread which is richer in proteid than most other kinds; but the dark colour of the loaf makes it unpopular. Various schemes have been devised to utilise the germ and the bran, which are ordinarily discarded. In the preparation of Hovis flour the separated germ is partially cooked by superheated steam. This kills the ferment contained in the soluble proteids, and thus prevents it from changing starch into maltose and dextrin. The action thus prevented is represented by the following formula:—

STARCH.MALTOSE.DEXTRIN.
10 C₁₂H₂₀O₁₀ + 6 H₂0 = 6 C₁₂H₂₂O₁₁ + 4 C₁₂H₂₀O₁₀.

The germ thus treated is ground to a fine meal, of which one part to three of ordinary flour, forms Hovis flour. Other ‘germ breads’ are also in the market. In the making of Frame food the bran is boiled with water under high pressure. The watery extract, containing the mineral and part of the nitrogenous constituents of the bran, is evaporated to dryness, and forms the basis of various preparations. It is doubtful if this food possesses any great value.

Brown bread is a somewhat vague expression, meaning either an admixture of bran or of germ or of both with flour, or bread made from whole wheat flour. In each of these cases the loaf would be brown. The bran is rich in fat as well as in phosphates. It acts as a mechanical irritant, ill borne by delicate stomachs, but very useful where a tendency to constipation exists. The excess of nitrogenous matter in brown bread and its richness in fat, do not prove its greater nutritiveness, as it is present in a condition in which only a portion is absorbable from the alimentary canal into the circulation.

The harder wheats, such as Sicilian wheat, contain a larger percentage of gluten; and from them macaroni and vermicelli are obtained, which are nearly pure gluten. They are very nutritious and useful foods. Semolina is prepared from wheat, the millstones being left sufficiently apart to leave the product in a granular condition. In malted breads, a syrupy infusion of malted barley (malt extract) is added to the flour. Malt extract contains in addition to malt sugar (maltose) and dextrins, a ferment (diastase) which, like the saliva, is able to convert starch into the soluble substances, maltose and dextrin (see formulæ above). The action of this ferment is stopped by the temperature of baking. Hence even when the malt extract is allowed a considerable time for its operation on the dough, only about 10 per cent. of the starch in the loaf becomes soluble, as compared with 4 per cent. in an ordinary loaf.

Oatmeal, obtained from the common oat, contains very little gluten, and so cannot be made into vesiculated bread. It contains a large proportion of other nitrogenous material and of fat. As porridge and oatmeal cake it forms a very nutritious diet. The husk ought to be carefully removed from the meal intended for human food, as, although very nitrogenous, it acts as a mechanical irritant. Groats consists of oats from which the husk has been entirely removed. The substitution of rolling for grinding in preparing oats for food and the application of heat during the rolling process, have made oatmeal more digestible, as in Quaker, Provost, and Waverley oats.

Barley contains very little gluten; on this account, like oatmeal, it does not admit of being made easily into bread.

Malt is barley which has been made to germinate by heat and moisture and then dried, “diastase” being formed in the process. Extract of malt, containing diastase in an active condition, is useful in cases of impaired digestion and deficient assimilation of food.

Rye is rarely used in this country for making bread. In Germany it is known as “black bread,” but its colour and acid taste make it disagreeable, and it is laxative in its action.

Maize, or Indian Corn, is deficient in gluten, and so not suitable for making vesiculated bread. Like oatmeal, it is made into cakes, called in America “Johnny cake.” It contains much fatty matter, and is largely used for fattening poultry and other animals. Oswego flour and corn flour are maize flour deprived by a weak solution of soda, of its proteids and fat; hominy contains all its constituents. Maize is a cheap and nutritious food. When wheat flour is dear, it is occasionally adulterated with maize. The adulteration can be detected by the forms of the starch granules, examined under a low power of the microscope.

Rice contains less proteids and fat than any other cereal. Its chief value as a food depends on the large amount of starch it contains (table, page [16]).

Leguminous Foods.—The chief seeds belonging to this group are peas, beans, and lentils. They contain a smaller proportion of starch, and a larger proportion of nitrogenous materials than cereals. Thus while flour contains 9.5 and bread 8 per cent. of proteid, lean meat 15.18 per cent., and cheese about 30 per cent., peas and beans contain 21 to 26 per cent. (green peas only 4 per cent., dried peas 21 per cent.) of proteid. The nitrogenous material exists chiefly as legumin, which has been called vegetable casein. Although leguminous seeds contain more nutritive material in a given weight than cereals, dietetically they are inferior, owing to the fact that they are less digestible, often causing flatulence and other dyspeptic symptoms. Cereals, again, are more palatable than leguminous seeds, and are more prolific, and consequently cheaper. In the absence of animal food, legumens form a useful substitute. They are advantageously diluted with oily substances, or with rice. The farm-labourer’s dish of broad beans and fat bacon is founded on strict physiological principles. A mixture of lentil and barley flour is sold under the name of Revalenta Arabica. Lentil flour costs 2½d., Revalenta 3s. 6d. per lb. Green peas, French beans, and scarlet runners are much more easily digested than are dried peas or beans. Lentils contain the largest proportion of proteid of any of the pulses. They also contain very little sulphur, and so do not give rise to the same liberation of sulphuretted hydrogen in the intestine, as other pulses. The ash of the Egyptian lentil is particularly rich in iron.

Amylaceous Foods. Amylaceous or starchy substances are contained in many of the preceding foods; but some other foods consist almost entirely of starch. The chief of these are sago, tapioca, and arrowroot.

Sago is obtained from the pith of the stems of various species of palm; a single tree may yield several hundred pounds. Alone it is easy of digestion. Boiled with milk it forms a light, nutritious, and non-irritating food. Fictitious sagos are frequently sold, made from potato starch.

Tapioca and Cassava are derived from the tubers of more than one species of the poisonous family, Euphorbiaceæ. The juices are removed, and the prussic acid removed by heat. Tapioca only differs from cassava in being a purer form of starch; the latter is more nutritious, and among the Indians takes the place of bread.

Arrowroot is obtained from the tubers of Maranta Arundinacea.

Tous-les-mois is a form of starch obtained from the tubers of a West Indian plant, the Canna edulis.

Fig. 1.—Different Forms of Starch Granules.
Potato. Wheat. Rice.
Oats. Barley. Pea.

The detection of the varieties of starch is usually possible owing to their fairly characteristic appearance under the microscope. Fig. 1 shows the most important starches. It must be noted that in oats, maize, and rice the contour is completely marked by facets or surfaces, while there are less complete markings in tapioca and sago. In wheat, rye, pea, bean, barley, potato, and arrowroot the contour is even, though there are minor differences of size and shape.

Other Vegetable Foods.—Green Vegetables contain comparatively little nutriment, but form valuable additions to other foods. Cellulose, which forms their main constituent, although indigestible, forms a bulk in the alimentary canal, which is necessary to ensure peristalsis. Concentrated nourishment can only be digested in limited quantity, and is very apt to produce digestive disorder. Cabbage contains 92 per cent. of water, and 2½ per cent. nitrogenous matter. Carrots contain 6 per cent. and turnips 2 per cent. of nitrogenous matter; parsnips are intermediate between these. Green vegetables possess valuable anti-scorbutic properties. They may be made an important vehicle for giving fatty food, by adding butter, etc.

Rhubarb and sorrel contain oxalates and tartrates of potash and lime, to which they owe their tartness. Spinach is cooling and laxative, like rhubarb, but not tart. Sea-kale, artichoke, and asparagus are all wholesome vegetables. Asparagus is somewhat diuretic, and gives a peculiar, disagreeable odour to the urine. Salads, such as mustard and cress, water-cress, endive, and the garden lettuce are very useful as anti-scorbutics. Some of them possess a peculiar pungency due to a volatile oil analogous to that contained in horse-radish.

The Potato contains 26 solid parts in 100, of which nearly 20 are starch and 2½ nitrogenous matter. It forms one of our best-appreciated vegetable foods, and as it possesses valuable anti-scorbutic properties, its universal use is, perhaps, the chief cause of the present rarity of scurvy. Alone, it possesses too small a proportion of nitrogenous material to support life, but the addition of butter milk makes up this deficiency; and these two together form a sufficient diet to maintain life and health for a long time.

The Onion, Garlic, Leek, and Shalot, all members of the lily family, are chiefly used as condiments. They contain an acid volatile oil, which gives them a peculiar odour and flavour. By long boiling, this is dissipated (as in the case of the Spanish onion), and the onion is then fairly digestible, as well as nutritious.

Celery possesses a more delicate flavour and odour than the preceding, but even the most tender celery is digested with difficulty; less so, when boiled or stewed, or a constituent of soups.

Only four Fungi are, with us, commonly regarded as safe—mushrooms, champignons, morels, and truffles; but there are many others which are equally edible. The food value of fungi has been exaggerated. They are difficult of digestion and contain little nutritive material. Poisonous fungi usually have an astringent styptic taste and a disagreeable pungent odour. In any doubtful case it is better to abstain.

Oily Seeds contain a considerable amount of fixed oil which renders them unfit for persons of weak digestion. The almond, walnut, hazel-nut, and cocoa-nut are common examples. The sweet almond, when eaten unbleached, occasionally produces nettlerash, and its solid texture and large proportion of fixed oils render it difficult of digestion. The chestnut contains less oil, but a large amount of carbohydrate. It is extensively used as a food in Italy and some other countries. In the uncooked condition it is very difficult of digestion.

Fruits are chiefly used as adjuncts to other foods; but the vegetable salts and the cellulose and sugar which they contain, make them very valuable. Cucurbitaceous fruits are used as vegetables rather than as fruits. Vegetable marrow is wholesome and agreeable, but not very nutritive. Cucumber is most digestible when rapidly grown and freshly gathered.

Stone-fruits or drupes, such as the peach, nectarine, plum, cherry, are rather luxuries than foods, like many other fruits. Before ripening they are unfit for food; when ripening is complete, the acids and astringent matter largely disappear. The date contains chiefly sugar, and forms an important food in the East.

Pomaceous Fruits, as the apple, pear, and quince, are more digestible when cooked; and, speaking generally, all fruit not perfectly ripe should be cooked before eating. The presence of vegetable acids in fruit soon converts the sucrose of cane sugar into dextrose, a less sweet variety of sugar. It is therefore more economical to sweeten after than before cooking.

The chief Berries are the grape, currant, gooseberry, cranberry, and elderberry. The grape is the most important, and 1,500 varieties of it have been described. Its juice contains a large amount of grape sugar (dextrose), and small quantities of glutinous material, bitartrate of potash, tartrate of lime, malic acid, etc.

Besides the above fruits, we have strawberries, mulberries, figs, plantains, melons, etc., which are all refreshing and anti-scorbutic. The orange family furnishes us with the orange, lemon, citron, lime, shaddock, and pomelo, of which the orange is by far the most important, and possesses most valuable refreshing qualities.

Sugar exists in two chief forms, viz. sucroses and glucoses. Sucroses, known chemically as disaccharids (Sucrose = C₁₂H₂₂O₁₁; compare starch = C₁₂H₂₀O₁₀) are exemplified in cane, beet, maple, malt (maltose), and milk sugar (lactose). Cane sugar has been gradually displaced by beet sugar. The two are chemically identical, and equally nutritious. Maltose is given in malt extract as a food, and because of the digestive action of the ferment also contained in the extract on starchy food. Thus:—

STARCH.MALTOSE.
C₁₂H₂₀O₁₀ + H₂O = C₁₂H₂₂O₁₁.

Lactose is comparatively free from sweetness, and is hardly capable of being fermented by yeasts.

Of Glucoses the best example is dextrose = C₆H₁₂O₆, H₂O, which can be seen crystallised in dried raisins; it only possesses one-third the sweetening power of sucrose. Starchy food becomes changed into glucose by the action of saliva and pancreatic juice in the alimentary canal. Grapes, cherries, gooseberries, figs, and honey contain lævulose in addition to glucose (glucose = C₆H₁₂O₆, H₂O, lævulose = C₆H₁₂O₆). Lævulose resembles dextrose except in being uncrystalline, and in its effect on polarised light. Many ripe fruits, such as pineapples, strawberries, peaches, citrons, contain sucrose and lævulose, the latter being not quite so sweet as sucrose.

In the alimentary canal sucroses are inverted into dextrose and lævulose. Thus natural foods containing these sugars are more readily assimilated than those containing sucrose.

The sweetening power of the varieties of sugar depends on their degree of solubility in water. Sucrose is soluble in one-third of its weight of cold, and in rather more of hot water. Dextrose is soluble in its own weight of water; lævulose is more soluble, and therefore sweeter than dextrose. Lactose requires five to six parts of cold and two of hot water, and is therefore not so sweet as the other varieties.

[CHAPTER IV.]
DISEASES DUE TO FOOD.

Diseases may arise from the noxious character or from deficiency or excess of some particular food, or of the food as a whole.

Diseases from Unwholesome Food.—I. The Meat of Diseased Animals.

(1) The flesh of animals which have not been slaughtered should be prohibited from sale, whether death has resulted from accident or disease. The meat from diseased animals is also generally dangerous, sometimes owing to the drugs with which the animals have been dosed before death, e.g. tartar emetic, or opium.

(2) Meat may be unwholesome from the presence of parasites. Of these the most common is—

(a) The cysticercus cellulosæ, which is the undeveloped embryo of the tape-worm; that from the pig becomes the tænia mediocanellata. The cysticercus of the pig is the most common; it forms a cyst about the size of a hemp-seed, commonest on the under surface of the tongue. In hams oval holes are found or opaque white specks, which are the remains of the cysts converted into calcareous matter. When meat containing the cysticercus alive (as in under-cooked or raw meat) is swallowed, it develops into the tape-worm, which consists of a number of flat segments, each capable of producing numerous ova of new cysticerci, with a minute head at the narrow end surrounded by hooklets. A temperature of 174° F. kills the cysticercus. Another kind of tape-worm common on the continent, called bothriocephalus latus, is derived from the cysticercus of fish.

Fig. 2.
Cysticercus (“Measles”) in Pork.
(Natural Size.)

(b) The trichina spiralis is not a solid worm like the tænia, but possesses an intestine. In pork it forms a minute white speck, just visible to the naked eye, which forms a nest, and in this one or two coiled up worms can be seen by a magnifying glass in active movement. They are effectually killed by the temperature of boiling water; but no form of drying, salting, or even smoking at a low temperature is sufficient for this purpose. Boiling or roasting does not suffice to destroy all the trichinæ unless the joint is completely cooked in its interior. When trichinous pork is swallowed, the eggs develop in the alimentary canal in about a week into complete worms, and in three or four days more each female produces over a hundred young ones. These burrow into every part of the body, producing great irritation and inflammation. In one case after death upwards of 50,000 worms were estimated to exist in a square inch of muscle. Most of the cases of trichinosis have occurred in Germany, from eating imperfectly cooked sausages. The pig becomes trichinous by eating offal, and man is infected by eating pork. This disease is rare in England.

Fig. 3.
Trichinæ Capsulated in Flesh.
Magnified.

(3) Tuberculous Meat, from animals suffering from tuberculosis, has been found to cause tuberculosis in small animals experimentally fed on it. Koch has recently thrown doubt on the communicability of bovine tuberculosis to man; but this point must be regarded as still unsettled (see page [312]). Sheep are rarely affected by it, but it is very common in cattle, especially in cows, and it is a serious economical question whether the meat of all such animals should be condemned. The ideal would be to condemn all such animals, as tuberculosis is an infective disease, and the bacillus which causes it (as well as the toxic products of its activity) may be present in meat which shows no actual signs of disease, except in the lungs or other internal organs. In practice, however, the rules laid down by the Royal Commission on Tuberculosis, in 1898, should be followed for the present. These state that:—

“The entire carcase and all the organs may be seized (a) when there is miliary tuberculosis of both lungs, (b) when tuberculous lesions are present on the pleura and peritoneum, or (c) in the muscular system, or in the lymphatic glands embedded in or between the muscles, or (d) when tuberculous lesions exist in any part of an emaciated carcase. The carcase, if otherwise healthy, shall not be condemned, but every part of it containing tuberculous lesions shall be seized (a) when the lesions are confined to the lungs and the thoracic lymphatic glands, (b) when the lesions are confined to the liver, (c) or to the pharyngeal lymphatic glands, or (d) to any combination of the foregoing, but are collectively small in extent.” They also add that any degree of tuberculosis in the pig should secure the condemnation of the entire carcase, owing to the greater tendency to generalisation of tuberculosis in this animal; and that in foreign meat, seizure should ensue in every case where the pleura has been “stripped.” (See also page [312].)

(4) Other Infective diseases besides tuberculosis may render meat wholly or partially unfit for food. Of these pleuro-pneumonia may not require condemnation of the entire carcase; but in the following this course should be adopted, cattle-plague, pig typhoid (pneumo-enteritis), anthrax, and quarter ill, as well as in sheep-pox. In puerperal fever, actinomycosis, and sheep-rot (liver flukes) each case must be decided on its merits.

II.—Decomposed Meat.—Putrid meat has often produced diarrhœa and other severe symptoms. Putrid sausages are especially dangerous, and incipient putridity seems to be more dangerous than advanced.

Tinned Meats occasionally produce severe illness, which has been in several cases fatal. It is important to secure a good brand, and to eat the meat as early as possible after the tin is opened. Tins in which any bulging is present, showing the presence of putrefactive gases, must be rejected; and still more tins which have been pricked and resoldered in a second place. All tinned meats and fruits are stated by Hehner to contain compounds of tin in solution. These do not seem to be perceptibly injurious, unlike lead salts, which are now rarely found.

The general subject of Meat Poisoning has had much light thrown on it during the last few years. Brieger, about 1886, showed that during the cultivation of bacteria, alkaloidal bodies known as ptomaines and leucomaines, were formed, which were virulently poisonous. It was commonly supposed that the poisoning occasionally produced by eating meat pies, sausages, hams, brawn, and similar food, was due to these ptomaines. It is now known, however, that there are far more important toxines than the alkaloidal, which result from bacterial life in meat, etc. (see page 286). These are more closely related to substances of an albuminous or proteid nature than the ptomaines. These toxines may be fatal when as small a dose as a fraction of a milligramme (mgm. = about ¹ ∕ ₆₄ grain) is given subcutaneously. The evidence now shows that neither ptomaines nor other toxines (albumoses) or any other bacterial products besides these, cause the outbreaks of acute poisoning occasionally traced to food, but that these are due to bacteria. There is, in other words, actual infection, as well as poisoning. The microbe chiefly found as the cause of these outbreaks is the Bacillus enteritidis of Gaertner, and some allied microbes. In an outbreak at Oldham, 160 pies made on a Thursday, from the veal of a calf killed on the preceding Tuesday, were baked in several batches, and of the persons eating these pies fifty-four became ill. That the contamination was not introduced after cooking was shown by the fact that several persons were made ill who ate pies still warm from baking. The facts indicated that one batch was imperfectly cooked, the time allowed being only twenty minutes, as compared with fifty minutes allowed in corresponding cooking in domestic life. Experimentally it has been found that an exposure for one minute to 70° C. kills the Bacillus enteritidis of Gaertner. That this bacillus was the cause of the outbreak was subsequently shown by the fact that the serum of blood taken from some of the patients showed characteristic clumping with a pure culture of this bacillus, just as happens with the blood of a patient suffering from enteric fever when a cultivation of the microbe of this fever is mixed with it (see page [301]). In this outbreak the symptoms were usually diarrhœa, vomiting, intense thirst, desquamation of the skin, and a slow convalescence, lasting from three to six weeks. (See page [26] for poisoning by Bacillus enteritidis sporogenes.)

III.—Meat injuries from the food eaten before killing.—Pheasants fed on laurel, hares on rhododendron chrysanthemum, and other animals fed on the lotus, wild cucumber, and wild melon of Australia, have caused dangerous symptoms.

IV.—Fish, especially some kinds, occasionally produce nettlerash and other disorders, especially in warm weather. Leprosy has been ascribed to the eating of decomposing fish, but it occurs in countries where a fish diet is impossible.

Shell-fish and crustaceans (as lobster, crab) are very prone to produce evil results. Shell-fish (mollusca), such as mussels, cockles, and oysters, are dangerous foods. They are generally grown in estuaries, to which the sewage of towns has access; and not infrequently cases of enteric (typhoid) fever, as well as more acute attacks of diarrhœa and vomiting, have been traced to them. Mussels and cockles are seldom sufficiently cooked to render them safe; and oysters are eaten raw. They should never be eaten, unless from personal direct knowledge it is certain that they have been derived from an estuary in which there was no possibility of contamination by sewage.

V.—Milk has been a common carrier of disease. Cows eating the rhus toxicodendron get the “trembles,” and their milk produces serious gastric irritation in young children. The milk of goats fed on wild herbs or spurgeworts has produced severe disorders.

The milk of animals suffering from foot-and-mouth disease, although frequently drunk with impunity, occasionally produces inflammation of the mouth (aphthous ulceration). The milk derived from cows fed on grass from sewage farms is, per se, as wholesome as any other, and its butter has no more tendency to become putrid than that derived from any other source.

The great dangers in respect to milk are of its becoming mixed with contaminated water; or of its absorbing foul odours. The absorptive power of milk for any vapour in its neighbourhood, is shewn by exposing it in an atmosphere containing a trace of carbolic acid vapour: the milk speedily tastes of the acid.

Milk also tends to undergo rapid fermentative changes, especially in warm weather, or when tainted by traces of putrefying animal matter. Diarrhœa in children is frequently due to such a condition, or to the rapid decomposition of milk in an imperfectly cleaned bottle. Milk should always be boiled in warm weather; and it should never be stored in ill-ventilated larders, or where there is a possibility of the access of drain effluvia; nor ought it to be kept in lead or zinc vessels.

Epidemic diarrhœa has been ascribed by Klein to a microbe called the Bacillus enteritidis sporogenes. This is not killed by heating the liquid containing it to 80°C. for twelve to fifteen minutes, as is the typhoid bacillus and other non-spore-forming bacilli. In an outbreak of diarrhœa among the patients in St. Bartholomew’s Hospital, London, there was strong evidence that this microbe taken in rice pudding had caused the mischief. Eighty-four patients and two nurses were attacked, and the patients who had eaten rice pudding were almost exclusively attacked. A portion of this pudding after being kept twenty-four hours was found sour and acid. The Bac. enteritidis sporog. was found in it. Furthermore it was shewn that the temperature at which the rice puddings were cooked never exceeded 98°C., whereas the spores of this microbe withstand 100°F. a considerable time.

Very many epidemics of enteric fever and scarlet fever, and a smaller number of epidemics of diphtheria have been traced to contaminated milk. Usually in enteric fever the contamination of the milk was traced to the use of water “for washing the milk-cans,” derived from specifically polluted sources, and doubtless the water was the real source of the disease. In most of the milk outbreaks of scarlet fever, either there was scarlet fever in the dairy, or persons employed in the dairy were in attendance on patients suffering from the disease; but in an outbreak connected with a supply of milk from Hendon, it was suspected that a certain eruptive disease of the udders of the cow might have been the cause of scarlet fever in man, without infection from a previous case of the disease. This point is still sub judice.

Tubercular disease of the intestines and mesenteric glands may be produced by taking milk derived from tuberculous cows. This was proved in the case of calves (page [311]), and there are strong reasons for thinking that the same is true for infants, though doubt has been thrown by Koch on the communicability of bovine tuberculosis to the human being. The only safe plan is to sterilise the milk (page [13]).

VII.—Vegetable Food (especially greens) is indigestible if stale, and all mouldy vegetables are dangerous. Over-ripe and rotten fruit is liable to produce diarrhœa; but the diarrhœa prevalent in summer is due much less to this than to other decomposing foods, particularly milk.

Poisonous symptoms have been produced by the admixture of darnel (lolium temulentum) with flour.

The eating of damaged maize in Italy is the cause of an endemic skin disease, called pellagra, which commonly proves fatal.

Ergotism is due to the growth on cereals (and most commonly on the rye) of a poisonous fungus, the claviceps purpurea, which produces a deep purple deposit on the grain. If bread made from such flour is eaten for prolonged periods, severe symptoms result; in some cases, a dry rotting of the limbs. There have been several epidemics on the continent, due chiefly to eating bad rye bread.

Starvation Diseases.—Simple Starvation causes death in a period varying with the previous state of nutrition. Usually death occurs when the body has lost two-fifths of its weight, whether this be after days, months, or years (Chossat). A supply of water prolongs the duration of life, to as much as three times what it would otherwise be. Good nourishment doubles the power of resisting disease; while deficient food prepares the way for many diseases. A large share of the decline in the English death-rate during the last forty years is due to free trade, and the great cheapening of wholesome food which has resulted from it.

An ill-balanced is more frequent than a deficient diet. Deficiency of fat is more serious than deficiency of carbohydrates, and deficiency of proteid is most serious.

Scurvy is caused by the absence of fresh vegetables. The use of the potato and the orange, as well as of lime juice (the juice of citrus limetta), has led to its extinction among adults in this country. In former times, it caused more deaths among seamen than all other causes put together, including the accidents of war. In infants fed upon tinned foods, whether condensed milk or patent foods, a form of scurvy still occurs. Infants fed on new-milk never suffer in this way. If, therefore, it is necessary to feed an infant on condensed milk for many consecutive months, potato gruel or raw meat juice or fresh milk must occasionally be given.

Rickets is chiefly due to improper feeding in childhood. The substitution of artificial foods (most of them containing starch) for the natural milk is its chief cause. The lower incisor teeth of an infant appear between the sixth and seventh months. Starchy food given before this age is undigested. Such food likewise leads to less fat and proteid being given, which are essential for growth. Deficiency of lime salts in the food does not cause it, and giving them in food or medicine will not cure it. Enrichment of the diet by cream or failing this by cod liver oil is the best means of preventing and curing it. Abundant fresh air and warm clothing are also necessary.

Relapsing fever generally follows epidemics of typhus fever, and is greatly favoured by starvation. Ophthalmia has been chiefly prevalent in charity schools in which the children are underfed, though its essential cause is contagion.

Diseases Connected with Over-Feeding.—A fire may go out for want of fuel, or from becoming choked with ashes; and it is the latter state of things which occurs in Gout and allied diseases. Weakness is commonly complained of, but this is due to excess of food embarrassing vital action; and abstinence and exercise are required to restore the balance. Excess of nitrogenous food—especially if combined with the use of sweet, or strong, or very acid wines, and beer—is particularly prone to produce gout. In these cases, animal food should only be taken once a day, and vegetable food should be allowed to preponderate.

Obesity is favoured by excess of starchy food and sugar, and by copious drinking of water or other beverages. The plan of curing obesity by restricting oneself almost entirely to meat food is only advisable, however, under certain conditions. Gall-stones are favoured by rich foods and excess of sugar; also by alcoholic indulgence. Dyspepsia is commonly due to loading the stomach at too frequent intervals; but on the other hand, it not infrequently leads to the taking of insufficient food, because of the discomfort produced. The result of this is that a chronic starvation results, with impaired vital powers. Dyspeptic patients should abstain from pastry and from tea and coffee, except in small quantities. Alcohol in any form, as a rule, does harm. Not uncommonly mastication is imperfectly performed, and a good dentist may cure the indigestion which has resisted all other treatment.

[CHAPTER V.]
DIET.

The importance of a duly proportioned and sufficient dietary is shown by its great influence on health and constitution. An ill-proportioned or deficient diet is certain to lead to failure of health. The anatomy of an animal may be modified in the course of generations by altered diet, as well as its character; thus, the alimentary canal of the cat has increased in length to adapt it to its omnivorous habits. In the case of the bee we have a still more remarkable instance. If by any accident the queen bee dies, or is lost, the working bees (which are sexually undeveloped) select two or three eggs, which they hatch in large cells, and then feed the maggot on a stimulating jelly, different from that supplied to the other maggots, thus producing a queen bee.

The food of mankind varies naturally with—

I.—Climate. A cold climate leads to increased metabolism, and consequently a large amount of fatty matter can be eaten without producing nausea. Witness the difference between a Laplander’s and a Hindoo’s diet.

The season of the year has likewise some influence. Vital processes are more active in spring than autumn, and more food is consequently required in the former season.

II.—Occupation. Although muscular exercise is not associated with an immediate increase of elimination of urea, yet as a matter of experience more nitrogenous food is required and can be metabolised by hard workers than by idlers. The trappers on the North American prairies can live for weeks together on meat alone, accompanied by copious draughts of tea. They are constantly in the open air, undergoing fatiguing exercises, in a dry and rare atmosphere. For brain workers no special food is required. Foods containing phosphorus have no special value, so far as is known, for mental work. Such work, however, is apt to affect digestion; consequently the digestibility of food is more important for those engaged in sedentary occupations than its chemical composition.

III.—Sex. As a rule, women require about one-tenth less food than men, but probably this rule hardly holds good in the case of women engaged in laborious work.

IV.—Age. Infants require only milk, and the less they have of any other food before a year old the better. Atwater has calculated that——

• A child under 2 requires ³ ∕ ₁₀ the food of a man doing moderate work.
• A child of 3 to 5 requires ⁴ ∕ ₁₀ the food of a man doing moderate work.
• A child of 6 to 9 requires ⁵ ∕ ₁₀ the food of a man doing moderate work.
• A child of 10 to 13 requires ⁶ ∕ ₁₀ the food of a man doing moderate work.
• A girl of 14 to 16 requires ⁷ ∕ ₁₀ the food of a man doing moderate work.
• A boy of 14 to 16 requires ⁸ ∕ ₁₀ the food of a man doing moderate work.

Vital processes are more active in early life, and food is required not only to carry on the functions of the body, but also to furnish the materials for growth. Hence, while the proportion of proteids to carbohydrates and fats should be—

As 1:5.3 in adults, it should be about as 1:4.3 in children.

After the age of thirty-five or forty, the tendency is to take too much food. All the tissues of the body are established, and excess of food (especially nitrogenous food) is liable to produce tissue degeneration by loading the system with partially metabolised matter, and may lead to gouty diseases. It is much safer to take what may be regarded as too little than too much food after this period.

Times for Eating.—The best arrangement seems to be to have three meals, each fairly nutritious, and containing all the constituents required. The Romans only had two meals daily, prandium and cœna. This is common among the French at present, but it tends to overloading the digestive organs at these meals.

An ordinary full meal has usually passed from the stomach in four hours. Fresh food ought never to be introduced before this period; it is advisable to allow an interval of five hours between meals for the healthy, so as to give time for the digestive organs to rest, and for the absorption of food. The practice of taking tea with the chief meal, or a “meat tea,” is bad. Tea is better taken an hour or two after food.

Regularity in the time of taking meals is important, as the digestive organs acquire habits like other parts of the body. Work ought not, if possible, to be resumed immediately after meals, nor active exercise of any kind. These tend to abstract blood from the digestive organs, and so diminish the efficiency of digestion.

Vegetable and Animal Foods.—The fact that the food we require can be obtained from the vegetable world has led to the proposition that vegetable food should be taken alone. It is urged in favour of this plan, that a large amount of suffering to animals would be prevented. Also that animal food is not so economical as vegetable, land being more economically employed in producing corn than in feeding cattle. Thirdly, there is the indubitable fact that health can be maintained for prolonged periods on vegetable food (including nuts, cereals, fruits, etc.)

On the other hand, the chief objections to a purely vegetable diet are that the undigested refuse is greater than with an equal quantity of animal food; that a longer time and more exertion than for animal foods are required in digesting the most nutritious vegetable foods, such as legumens, while other vegetable foods do not contain a sufficient proportion of nitrogenous material. Also, if one lived entirely on vegetable food, a greater bulk would be required, and owing to the fact that such food is less easily absorbed, satisfaction to the appetite would not so soon be produced. Animal food has a great advantage as regards convenience. Man is not an eating machine; he requires food which is easily converted into the body substance, and this is supplied by the flesh of animals, milk and eggs, with a due proportion of non-nitrogenous food; sheep and oxen work up indigestible vegetable materials into easily assimilable mutton and beef. The greater convenience of animal food as a supply of proteid is shown by the following examples of foods after the removal of water:—

On the other hand, vegetable foods are a cheaper source, not only of carbohydrates and fats, but also of proteids as well. Thus the approximate cost of—

Under the ordinary conditions of town life, there is considerable danger of indulging in an excess of nitrogenous food, and vegetarians may therefore do good by showing that meat is not absolutely necessary, and can often with advantage be largely replaced by vegetable food.

If we include milk, cheese, and eggs in the vegetarian diet, the objections to it partially disappear; and it would be well if it were much more widely known, especially among the poor, that on these, together with vegetables, health can be maintained with the addition of little or no meat.

The Determination of Diet.—The first principle in making a dietary is that it must be mixed, containing all the necessary constituents, proteids, hydrocarbons, carbohydrates, water, and salts. No one of these alone will support life for any considerable period. Carbohydrates (sugar and starch) can be most easily dispensed with; fats, on the other hand, are essential for the maintenance of health.

The next point is to ascertain the proportion in which these different foods are required. Salts are commonly taken with other foods, common salt being the only one taken alone. The amount required is given on p. 7. The amount of water required varies with the season of the year, the amount of exercise and perspiration, and other factors. As a rule, not more than two pints of water are required per day, and still less if fruit is freely taken. We may therefore confine our attention to the carbonaceous and nitrogenous foods, and try to ascertain the amount of each of these required. Every diet must be subjected to the following tests, to fully ascertain its value:—

1. The Chemical Test.—The metabolism undergone by food in the body being essentially a process of oxidation (though partially modified and incomplete), the amount of heat yielded on complete combustion of a food may be taken as a measure of its value as a source of energy, of which heat and work are convertible forms. The standard of heat production is the calorie, the amount of heat required to raise the temperature of one gramme of water 1° C. This is the small calorie. The kilo-calorie (called the Calorie) is the amount of heat required to raise 1 kilo (1 litre) of water 1° C., or 1 lb. of water 4° F. In calculations on this basis, allowance must be made for foods which are incompletely oxidised in the body. Rubner has shown that the heat value of 1 gramme (=15½ grains) of each of the chief food stuffs is as follows:—

The method of applying this standard to a food is as follows: the percentage of proteid or carbohydrate given in the following table is multiplied by 4.1, and the percentage of fat by 9.3:—

Thus for bread—

The total fuel value in Calories of one pound of certain typical foods is given by Hutchison as follows:—Butter 3,577, peas 1,473, cheese 1,303, bread 1,128, eggs 739, beef 623, potatoes 369, milk 322, fish (cod) 315, apples 238.

2. The Physiological Test.—Not only is a proper proportion of proteid, fat, and carbohydrates required, but these must be capable of digestion and absorption and of oxidation in the body. Cheese is a highly concentrated food, but its value is less than its percentage composition would indicate, because of the difficulty of digesting considerable quantities of it. Green vegetables consist largely of cellulose, which is only imperfectly capable of absorption into the blood, although it can experimentally be oxidised by combustion. The proportion between absorbed food and food rejected in the fæces can be ascertained by analysis. Many experiments made on these lines show that on a purely animal diet (meat, eggs, milk) but little nitrogen is lost, while with vegetable foods (carrots, potatoes, peas, etc.) the waste of nitrogen is considerable. Fats are very completely absorbed from the alimentary canal. The amount remaining unabsorbed is greatest with mutton fat (10 per cent.), least with butter (2½ per cent.). Experimentally it has been found that an amount up to 150 grammes (about 5½ oz.) of fat can be absorbed without appreciable loss. Carbohydrates are very completely absorbed, even starchy foods rarely escaping digestion. Completeness of absorption from the alimentary canal is not desirable for all foods; a certain amount of unabsorbed residue is required to stimulate peristalsis. With a purely vegetable diet this amount is excessive, and there is physiological waste of effort.

3. In practical dietetics the Economic test is important. Carbohydrate is by far the cheapest food, and generally vegetable are cheaper than animal foods. Thus a shilling’s-worth of bread yields 10,764 Calories, while the same sum spent on milk would only yield ¹ ∕ ₃, and on beef ¹ ∕ ₁₀ this number of heat units. Similarly a shilling’s-worth of peas contains 572 grammes of proteid, about double as much as the same money’s-worth of cheese; while to obtain the same amount of proteid from eggs would cost more than eight, and from beef more than five times as much as from peas (Hutchison). The market price of foods is no certain indication of their nutritive value. Thus haddock will supply as much nutriment as sole at a fourth of the cost; Dutch as much nutriment as Stilton cheese at less than half the cost. Similarly the most economical fats are margarine and dripping.

4. An Examination of Actual Dietaries under various conditions has strikingly confirmed the results obtained by other methods. It has been found that (a) the potential energy required by a healthy man weighing 11 stones, and doing a moderate amount of muscular work is 3,000 to 3,500 Calories (=310 grains); and that (b) about 20 grammes of nitrogen and 320 grammes (=4,960 grains) of carbon are excreted by such a man. (c) Expressing the 3,000 Calories required in terms of grammes of food, it is found that 125 grammes of proteid, 500 of carbohydrate and 50 of fat are necessary. These facts are expressed in the following table (Hutchison):—

Three of the best known standard dietaries give the amounts in grammes of each food constituent as follows:

Expressing the same facts in English ounces instead of grammes, ⁴² ∕ ₅ oz. of proteid, 2½ oz. of fat, and 18 oz. of carbohydrate, would represent the ounces of each constituent required according to

The chief point of divergence in the above standard dietaries is in the relative proportion of carbohydrate and fat. Probably the correct proportion between these is as 1 to 10; but it will vary according to climate and other circumstances. Detailed examination of a large number of dietaries shows that the amount of daily proteid should be about 125 grammes, or 4⅖ozs. This is contained in 20 eggs, or in 18 oz. i.e. about 4½ ordinary platesful of cooked meat.

It must be noted that the 23-24 oz. of food given above as the standard daily amount represents dry food. This represents 40 oz. or nearly 3 lbs. of ordinary food.

The following example by Waller, gives a rather liberal standard English diet, for a man doing a moderate amount of muscular work.

This divided up into meals works out roughly as follows (Hutchison):—

Breakfast		Two slices of thick bread and butter.
		Two eggs.
Dinner		One plateful of potato soup.
		A large helping of meat with some fat.
		Four moderate sized potatoes.
		One slice of thick bread and butter.
Tea		A glass of milk and two slices of thick bread and butter.
Supper		Two slices of thick bread and butter and 2 oz. of cheese.

From the preceding data, practical problems as to dietaries are easily solved. Thus if it be required to find
how much oatmeal, milk, and butter would be required to give a sufficient quantity of albuminoids, fats, and carbohydrates to an adult male,
the calculation may be based on the figures in the table on p. 32, or the following figures may, for the sake of convenient calculation, be taken as representing the percentage amount of each of these chief food principles contained in the foods named:—

• Let
• o = number of ounces of oatmeal required.
• m = number of ounces of milk required.
• b = number of ounces of butter required.
• Then
• (12o + 4m + 2b ∕ 100 = 4.5 ozs. of albuminoid
• (6o + 3m + 88b)/100 = 3 ozs. of fat
• (60o + 5m)/100 = 14.25 ozs. of carbohydrate,

according to Moleschott’s diet.

When these equations are worked out by substitution and transference—

• o = 19.2 ounces.
• m = 55.4 ounces.
• b = 0.24 ounces.

Similarly if it is required to find how much meat, bread, and butter of the following percentage composition will be required to give a man a sufficient amount of albuminoids, fats, and carbohydrates.

• Let
• m = number of ounces of meat required.
• b = number of ounces of bread required.
• B = number of ounces of butter required.
• Then
• (12m + 8b + 2B)/100 = 4.5 ozs. of albuminoid
• (15m + 1.5b + 88B)100 = 3 ozs. of fat
• 50b ∕ 100 = 14.25 ozs. of carbohydrates

When these equations are worked out—

• m = 6.28 ounces.
• b = 28.5 ounces.
• B = 1.15 ounces.

Relation of Food to Mechanical Work.—In the body the movements of every part are constant sources of heat. It is evident therefore that the potential energy of food can be expressed by (a) the amount of heat obtained by its complete combustion, or (b) by the amount of work capable of being obtained from it. Joule discovered by exact experiment that the mechanical power obtainable from a given amount of fuel is directly proportional to the amount of fuel used, being in fact due to the oxidation of this fuel, the heat produced being transformed into mechanical power. The heat unit or calorie has been already given (p. 32). The gram-metre is the work unit. The heat unit corresponds to 425.5 units of work. Thus the same energy required to heat one gramme of water 1° C. will raise a weight of 425.5 grammes to the height of 1 metre. Conversely a weight of 425 grammes if allowed to fall from a height of 1 metre, will by its concussion produce heat sufficing to raise the temperature of 1 gramme of water 1° C. In England the amount of work done is commonly expressed as foot tons, i.e. tons lifted one foot; while in France it is similarly expressed as kilogrammetres. Gramme-metres can be converted into foot-pounds by multiplying them by .007233, and kilogrammetres into foot-tons by dividing by 311.

Frankland estimated that—

In practical dietetics digestibility of food as well as chemical composition is an important factor. Furthermore metabolism in the body is not in every instance so complete as oxidation outside it. Hence estimates of potential energy can only be regarded as theoretically correct. Examination questions like the following are occasionally asked:—

A man does work equal to 176.8 foot-tons in a day. Supposing that he eats only bread, how much will he require to give the amount of energy required, if bread contains 8 per cent. proteid, 1.5 per cent. fat, and 49.2 per cent. carbohydrate?

On the above basis, from 100 ounces of bread the amount of potential energy obtainable is:—

Let b = number of ounces of bread required to develop 176.8 foot-tons of energy.

Then 8,601: 100:: 176.8: b.

Therefore b = 2.05 ounces.

[CHAPTER VI.]
THE PREPARATION AND PRESERVATION OF FOOD.

Objects of Cooking.—Food may be taken in its crude condition, as directly derived from the animal or vegetable world, or after it has undergone a preparatory process of cooking. Man is the only animal who cooks his food. Many foods, in the uncooked condition are almost entirely incapable of digestion by him—such as the proteid and farinaceous materials contained in the seeds of cereal and leguminous plants. But cooking, as a preparatory help to the digestion of food, is not equally required by all foods. Thus, fruit is commonly taken uncooked, and does not undergo any important alteration on cooking. Salads are taken uncooked, but not for their nutritive properties so much as for a relish to other foods, and for their quasi-medicinal properties. Milk, again, may be taken cooked or uncooked. The oyster is the only animal which is eaten habitually, and by preference, in the uncooked condition; and there is a physiological reason for this universal custom. The large fawn-coloured liver, which constitutes the delicacy of the oyster, is little else than glycogen, associated with its appropriate ferment diastase, so that the oyster is almost self-digestive. When cooked, the ferment is destroyed, and digestion of the oyster becomes more difficult.

Cooking is intended—1. To make the food softer, and in part to mechanically disintegrate it, thus rendering it more easily masticated and digested. In fact, cooking, in the best sense, is an artificial help to digestion; and digestion may well be said to commence in the kitchen.

2. To produce certain chemical changes. Thus, starch is partially converted into dextrine; gelatin is formed from connective tissue, etc.

3. To destroy any noxious parasites present in the food, or obviate any ill effects from putrefactive changes. Diseased meat chiefly produces bad effects when imperfectly cooked.

4. To make the food more pleasant to the eye and agreeable to the palate. The improved savour in cooked meat, for instance, has a very appetising effect, and consequently makes digestion easier.

The Cooking of Flesh.—1. Roasting is, perhaps, the most perfect way of cooking meat. It exalts its flavour more than any other method. In roasting, place the meat at first sufficiently near a brisk fire, so that the albumin on its surface may be readily coagulated, and the juices retained in the interior of the joint. After about fifteen minutes, the joint ought to be removed somewhat further from the fire, and allowed to cook slowly. Frequent basting is desirable to obtain a good result. Brown meats, such as beef, mutton, and goose, require a quarter of an hour per pound weight; veal and pork require about ten minutes additional, to ensure the absence of redness. White-fleshed birds require a somewhat shorter time. The time required in roasting will be a little more if the joint is large, or the fire not very clear. To ascertain if the meat is sufficiently cooked, press the fleshy part; if it remains depressed, it is done; if not done, it retains its elasticity. At the first incision, gravy should flow out of a reddish colour.

The changes undergone during roasting are, that the connective tissues uniting the muscular fibres is converted by the gradual heat into gelatin, which is soluble and easily digested; the muscular fibres, consequently, become more separable, and the myosin of which they consist is rendered more digestible. The fat is partly melted out of its fat cells, and partly combines with the alkali from the blood-serum. Empyreumatic oils (i.e. fat partially burnt), developed by charring of the surface of the joint, are carried off when it is roasted in front of the fire; and so, to a large extent, is acrolein. Acrolein (C₃H₄O) is always produced by the destructive distillation of neutral fats containing glycerine, and is the cause of the intolerably pungent odour accompanying the process. Osmazome, a peculiar extractive matter, on which the flavour and odour of meat depend, is developed better by roasting than by any other method of cooking.

It is useful to remember, in buying beef or mutton, that 20 per cent. must be allowed for bone and 20 to 30 per cent. for the loss during cooking.

The following figures are by Johnston:

Thus roasting is the least economical method of cooking. The chief loss, however, is of water; the dripping and gravy are recoverable.

2. Baking of meat in a closed oven does not produce so agreeable a result as roasting in front of an open fire. The oven ought always to be very hot before the meat is put in, in order to rapidly coagulate its surface. Baked meat may have an unpleasant flavour, owing to its saturation with empyreumatic oils, which escape in open roasting. The unpleasant flavour can be prevented by covering the meat with a layer of some non-conducting material, as a pie-dish or a crust, no empyreuma being then formed. Baked white of egg, as in the dish of fried ham and eggs, is one of the most indigestible forms of albumin obtainable.

3. Boiling of meat requires the same time as roasting. If the flavour and juices are to be retained, the joint ought first to be plunged into soft boiling water, and then, after three minutes, allowed to stand aside in water at 170° Fahr. The preliminary boiling forms a coating of coagulated albumin over the joint. Where there is no thermometer to guide the cooking—after the preliminary boiling for three to five minutes, add three pints of cold water to each gallon of boiling water, and retain at the same temperature for the rest of the process, i.e., at about 170° Fahr. If the meat is boiled in an inner vessel surrounded by water (water-bath), the temperature of the inner vessel does not rise above 160°-170° F. Ordinary “simmering” means that the meat is kept all the time at a temperature of 212° F. and is thus spoilt. The boiling of an egg is an example of the same point. If an egg is kept in water at a temperature of 170° F. for 10 to 15 minutes, its contents form a tender jelly, while an egg kept in water at 212° F. for the same length of time is hard and tough. An egg is more digestible when cooked in water at 170° F. for 10 minutes than when boiled in water for 2½ minutes.

The use of soft water for cooking purposes is always advisable; otherwise a longer period must be allowed. A preliminary boiling for a few minutes renders hard water softer, and the addition of a little carbonate of soda has a like effect.

When meat is inserted in water at a temperature below its boiling point, the juices are gradually extracted, while the meat is left a mass of indigestible fibres. A good soup is produced, but the meat is almost valueless. In order that the soups and broths may be nutritious, the less heat is employed in their preparation the better. If a soup is strained to make it clear, much of the most valuable part is removed.

Stewing is a process intermediate between boiling and baking. It possesses the great advantage over dry baking that no empyreumatic gases are produced, and there is no charring. The temperature of the stew-pan ought never to be above 180° Fahr.; at this heat the roughest and coarsest kinds of meat are made tender. The only objection to stewing is that the meat becomes saturated with fat and gravy, and is too rich for weak stomachs. It is advisable to stew lean meats only.

Hashing is a process of stewing applied to meat which has been previously cooked. The consequence of this double cooking, is that the meat becomes tough and leathery. A modified hash in which the meat is simply well warmed throughout is preferable.

Frying, unless carefully done, renders meat difficult of digestion, each fibre becoming coated with fat. The art is to “fry lightly,” that is, to burn quickly and evenly, so that no charring is produced. Two methods of frying are described. In the first, the substance to be fried, as an omelette or pancake, is placed with a little fat or oil in a frying-pan. This is really a modified process of roasting, the fat merely serving to prevent the object from adhering to the shallow pan. In the second, the substance to be fried is immersed in fat; for this purpose a frying kettle is required. Olive oil or good cotton seed oil is best for use in the frying-kettle. Lard is a bad material for frying; both it and butter are apt to burn unless heated slowly. Dripping is a good substance for frying. The fat used must be heated to from 350° to 390° F., and then the substance to be fried, e.g. a sole, plunged into it and left for two or three minutes. In this process the substance of the sole is really being steamed by the steam generated in the substance of the sole.

6. Broiling and Grilling are really processes of roasting applied to small portions of meat. In grilling, it is important that the gridiron should be hot before putting anything on it. An external coagulation of albumin is produced, as in good roasting and boiling.

The Cooking of Mixed Dishes.—A few instances may be given of common errors in preparing compound dishes. An egg in a custard, or just coagulated in a poached egg, is a light and easily-digested food; baked half an hour in a pudding, it is much less digestible; fried with ham, it is almost as indigestible as leather. Spices, if mixed with a dish before it is boiled, lose nearly all their flavouring power, while they remain irritating. They ought to be added near the end of the cooking process. A soup containing vegetables, as well as meat juices, should be prepared in two parts. The vegetables require prolonged boiling; gravy is spoilt by this. Similarly, the jam in a tartlet, if inserted before baking, loses its proper fruity flavour; and oysters baked in a beef-steak pie are indigestible.

The Cooking of Vegetable Foods.—Bread is either vesiculated or unvesiculated; the latter being what is called unleavened bread. Vesiculation of bread has usually been produced by fermentation of some of the sugar of the flour. The starch first becomes sugar (dextrose) and then the growth of the yeast plant in the dough splits this up into alcohol and carbonic acid gas. The carbonic acid percolates the substance of the dough, rendering it porous. When it has “risen” sufficiently, the dough is placed in the oven. The heat of the latter kills the yeast plant, thus preventing any further fermentation, but at the same time expands the carbonic acid gas in the bread, rendering the latter still more porous, and drives off in a gaseous condition the greater part of the alcohol produced by the previous fermentation.

It is objected to this plan of making bread, that a little of the sugar is wasted in producing alcohol and carbonic acid. To remedy this, another plan is sometimes adopted, as first proposed by Dr. Dauglish. In it the dough is charged with carbonic acid dissolved in water under considerable pressure. The gas escapes in the substance of the dough, and on baking expands as in the ordinary method of making bread. Bread made in this manner, is called “aerated bread.” Nevill’s bread has a solution of carbonate of ammonia incorporated in the dough, which is dissipated by heat, thus causing vesiculation of the bread.

On the continent, a mixture of hydrochloric acid and carbonate of soda is commonly used, carbonic acid and common salt being formed in the dough. Thus NaHCO₃ + HCl = NaCl + H₂O + CO₂. The hydrochloric acid employed should be perfectly pure and free from arsenic. Baking powders are also largely used for making cakes. “Self-raising” flour is flour with which baking-powder has already been mixed. Most baking-powders consist of a mixture of carbonate of soda and tartaric acid or bitartrate of potash, diluted with starch. When wetted, carbonic acid gas is evolved. A few contain alum, which is now an illegal material for this purpose.