THE CEREBRO-SPINAL SYSTEM.
The Nervous Tissue.
The nervous system consists of the cerebrum, pons varolii, cerebellum, medulla oblongata, the spinal cord with its nerves and the sympathetic ganglia, etc.
The cerebrum or brain proper constitutes the highest and much the largest portion of the encephalon. The cerebrum consists of two halves, that are connected with each other by the corpus callosum, and with the peduncular masses of the cruri cerebri, the processus a cerebello ad cerebrum; the series of eminences, or cerebral centers or ganglia, concealed from view, named corpora quadrigemina, optic thalamus and corpora striata, etc.
The cerebral hemispheres are by far the most bulky part of the cerebrum. Various commissural structures unite the two hemispheres, including the corpus callosum and fornix; and some smaller structures, viz., the pineal gland, the petuitary bodies, and the olfactory bulb.
The cerebral hemispheres together form an ovoid mass, in contact with the vault of the cranium, and with its smaller end forward, its greatest width being opposite to the parietal eminences. They are separated in the greater part of their extent by the great longitudinal fissure.
The surface of the hemisphere is composed of gray matter, and is molded into numerous smooth tortuous eminences, named convolutions, or gyri, which are marked off from one another by deep furrows, called sulci.
The cerebrum is divided into lobes for convenience of study, five in number, called frontal, parietal, occipital, temporal, sphenoidal, and central.
The internal structure of the cerebrum is composed of white matter. It consists of tubular fibers varying in size in various parts, but in general still smaller than those in the cord, their average diameter being 1⁄10000 of an inch. The fibers of white substance present no division. They are arranged in bundles, separated by a network of delicate connective tissue, consisting of cells, etc. The cells are of various forms and sizes—spheroidal, angular, fusiform, etc. The fibers radiate from the white center of each convolution in all directions into the gray cortex, having a course for the most part perpendicular to the free surface. In passing through the gray substance they are arranged in bundles about 1⁄1500 of an inch in diameter, thus separating some of the nerve cells, etc.
The olfactory tract and bulb, the corpora quadrigemina, corpora genicolate, optic thalamus, corpora striata, are all more or less mixed. They possess gray matter.
The nerves immediately connected with the brain are of several kinds. And there are twelve pairs of them. They are called cerebral nerves.
There are four kinds.
1. Nerves of special sense.
2. Nerves of common sensation.
3. Nerves of motion.
4. Mixed nerves of sensation and motion.
The nerves of special sense may with great propriety be termed the nerves of observation, perception—the gateways of intelligence and education.
I.—Nerves of special sense:
1. The olfactory supplies the nose, special sense of smell.
2. The optic supplies the eye, special sense of sight.
3. The auditory supplies the ear, special sense of hearing.
4. Part of the glosso-pharyngeal supplies the tongue and pharynx.
5. The gustatory, lingual branch of the fifth, supplies the tongue, sense of taste.
II.—Nerves of common sensation:
1. The ophthalmic supplies the eye.
2. The superior maxillary supplies the upper jaw and teeth.
3. The inferior maxillary supplies the lower jaw and teeth.
III.—Nerves of motion:
| 1. | The third nerve, motor acuti. |  | Supply the muscles of the eye. |
| 2. | The fourth nerve, trochlear or pathetic. | ||
| 3. | The fifth, branch of fifth. | ||
| 4. | The sixth, abducers. |
5. The facial nerve supplies the muscles of the face.
6. The hyperglossal supplies the muscles of the tongue.
IV.—Mixed nerves:
1. The pneumogastric supplies lungs, heart, stomach, larynx, etc.
2. The spinal accessory supplies some muscles of the back.
The average weight of the brain in the adult male is about 49½ ounces, a little more than three pounds avoirdupois; in the female 44 ounces; the average difference between the two being from 5 to 6 ounces.
The spinal cord has a length of about 16 to 17 inches, and weighs about 1½ ounces.
The spinal cord is a continuation of the medulla oblongata, is lodged in the spinal canal, and gives off 31 pairs of nerves, that supply all the muscles of the body with sensitive and motor nerves.
The medulla oblongata is pyramidal in form, having its broad extremity upwards. It is expanded laterally at its upper part. Its length from the pons varolii to the lower extremity of the pyramid is about an inch and a quarter; its greatest breadth is nearly an inch; and its thickness from before backwards is about three-quarters of an inch.
The medulla is the link between the brain and the spinal cord. The majority of centers for various organic functions are situated in it; as follows:
1. The respiratory center, with its neighboring convulsive center (venous blood excites convulsive centers, etc.). 2. The vaso-motor center. 3. The cardiac-inhibitory center. 4. The diabetic center, or center for producing artificial diabetes. 5. The center for deglutition. 6. The center for the movements of the æsophagus, with its vomiting center. 7. The center for reflex excitation of the secretion of saliva, with which may be associated the center through which the væjus (pneumogastric) influences the secretions of pancreatic juice, and possibly of the other digestive juices. 8. The center for the dilation of the pupil by means of the cervical sympathetic.
From the surface of the medulla certain of the cranial nerves arise, namely the sixth (abducens), glosso-pharyngeal, pneumogastric, spinal accessory, etc.
The fibers from the spinal cord pass upwards through the medulla oblongata and various other structures and finally reach the cerebrum.
The cerebellum, or hinder brain, consists of a body, and of three pairs of crura or peduncles, by which it is connected with the rest of the cerebro-spinal axis. The cerebellum is covered with a gray cortical substance, rather darker than that of the cerebrum. Its greatest diameter is transverse, and extends to about three and a half or four inches; its width from before backwards is about two or two and a half inches; and its greatest depth is about two inches, but it is much thinner round its outer border. It consists of two lateral hemispheres joined by a median portion called the vermiform process, and other structures therewith connected, etc.
Minute structure: The cortical gray substance is composed of an external clear gray layer, an inner grayish-red “granule” layer, and between the two a single layer of large cells with long processes, termed the corpuscles of Porkinge (after the man who first described them). Outside all is the layer of fibers and vessels of the pia mater. The external layer consists of a delicate matrix, probably of the nature of connective tissue, consisting of cells and fibers, etc.
The cerebellum is probably concerned in the coördination of movements. Its functions seem especially connected with afferent impulses proceeding from the semicircular coats.
The spinal cord is a cylindriform column of nerve substance connected above with the brain, through the medium of the medulla oblongata, terminating below, about the lower border of the first lumbar vertebra, in a slender filament of gray or vesicular substance, the filum terminale, which lies in the midst of knots of many nerves forming the codæ equina. Through the center of the cord, running in a longitudinal direction, is a minute canal, which is continuous through the whole length of the cord, and opens above into the space at the back of the medulla oblongata and pons varolii, called the fourth ventricle; the aqueduct of silvius connects it with the third ventricle, lateral and fifth ventricles, near the base of the brain. The cerebro-spinal fluid circulates in the interior of these ventricles and spinal cord. What precise mechanical function it subserves is only surmised, not known.
The cerebro-spinal axis is protected by three membranes, named also meninges. They are: 1. An external fibrous membrane, named dura mater, which closely lines the interior of the skull, and forms a loose sheath in the spinal canal; 2. An internal areolo-vascular tunic, the pia mater, which accurately covers the brain and spinal cord; and, 3. An intermediate membrane, the arachnoid, which lies over the pia mater, the two being in some places in close connection, and in others separated by a considerable space.
The sympathetic nerves are distributed in general to all the internal viscera, and to the coats of the blood-vessels. Some organs, however, receive their nerves also from the cerebro-spinal system, as the lungs, the heart, and the upper and lower parts of the alimentary canal.
The great gangliated cords consist of two series, in each of which the ganglia are connected by intervening cords. These cords are placed symmetrically in front of the vertebral column and extend from the base of the skull to the coccyx.
With respect to the functions of the sympathetic nervous system, it may be stated generally that the sympathetic nerve fibers are simple conductors of impressions as those of the cerebro-spinal system are, and that the ganglionic centers have (each in its appropriate sphere) the like powers of conducting and of communicating impressions.
The general processes which the sympathetic appears to influence, are those of involuntary motion, secretion, and nutrition.
Nerve centers. This term is applied to all those parts of the nervous system which contain ganglion corpuscles, or vesicular nerve-substance—i.e., the brain, spinal cord, and the several ganglia which belong to the cerebro-spinal and the sympathetic system. Each of these nervous centers has a proper range of functions, the extent of which bears a direct proportion to the number of nerve fibers that connect it with the various organs of the body, and with other nervous centers; but they all have certain general properties and modes of action common to them as nervous centers. The brain does not issue any force, except when itself impressed by some force from within, or stimulated by an impression from without; neither do the other nerve centers without such previous impressions produce or issue motor impulses.
The more certain and general office of all the nervous centers is that of variously disposing and transferring the impressions that reach them through the several centripetal fibers. In nerve fibers impressions are conducted only in the simple isolated course of the fiber; in all the nervous centers an impression may not only be conducted, but also communicated; in the brain alone it may be perceived.
In all cases in which the mind either has cognizance of, or exercises influence on, the process carried on in any part supplied with the sympathetic nerve, there must be conduction of impressions through all the nervous centers between the brain and the part. But instead of, or as well as, being conducted, impressions made on nervous centers may be communicated from the fibers that brought them to others, and in this communication may be either transferred, diffused, or reflected. Along nerve fibers impressions or conditions of excitement are simply conducted; in nerve centers they may be made to deviate from their course, and may be variously diffused, reflected, or otherwise disposed of.
Function of nerves. The office of nerves as simple conveyors or conductors of nervous impressions is of a twofold kind: 1. They serve to convey to the nervous centers the impressions made upon the peripheral extremities or parts of their course; 2. They serve to transmit impressions from the brain and other nervous centers to the parts to which they are distributed. For this twofold office of the nerves two distinct sets of nerve fibers are provided, in both the cerebro-spinal and sympathetic systems. Those which convey impressions from the periphery to the center are classed together as centripetal or afferent nerves, or nerves of sensation—sensitive nerves. Those, on the other hand, which are employed to transmit central impulses to the periphery are classed as centrifugal or afferent nerves or motor nerves, conveying impulses to the voluntary and involuntary muscles, etc.
Nerves are constructed of minute fibers or tubules full of nervous matter, arranged in parallel or interlacing bundles, which bundles are connected by intervening connective tissue in which their principal blood-vessels ramify.
The size of nerve fibers varies, and the same fibers do not preserve the same diameter through their whole length, being largest in their course within their trunk and branches of nerves, in which the majority measure from 1⁄2000 to 1⁄3000 of an inch in diameter. As they approach the brain or spinal cord, and generally also in the tissue in which they are distributed, they gradually become smaller. In the gray or vesicular substance of the brain or spinal cord they generally do not measure more than from 1⁄10000 to 1⁄14000 of an inch.
The chemical composition of nervous matter. Like most of the other tissues of the body, the nervous substance contains a large proportion of water (from three-fourths to four-fifths of its weight). Of the residue which remains after the removal of this by evaporation or other means, the larger part consists of a phosphuretted fat, which may be obtained crystallized, and in this condition was termed protagon. The crystalline substance, however, is in reality a mixture of two other substances, lecithin and neurin. Cerebrin is also described as being frequently met with in conjunction with lecithin.
| Lecithin. | Neurin. | Cerebrin. | Cholestrin. | |
| Carbon, | 44 | 5 | 17 | 26 |
| Hydrogen, | 90 | 15 | 33 | 44 |
| Nitrogen, | 1 | 1 | 1 | |
| Phosphorus, | 1 | |||
| Oxygen, | 9 | 2 | 3 | 1 |
CHAPTER XVIII.
FOOD AND FOOD-SUBSTANCES.
There are two kinds of food: 1. Those food substances that are derived from the animal kingdom; and, 2. Food substances that are derived from the vegetable kingdom.
Food is taken into the system to replace the material expended by the human body, or the waste products which are thrown off from the master tissues.
Definition: Food may be defined to be any natural substance, vegetable or animal, recognized as such, that has undergone neither the process of fermentation nor that of putrefaction.
Food may be considered in its relation to two purposes—the nutrition of the tissues, and the production of heat. Under the first of these heads will be included many other allied functions, as for example, secretion and generation; and under the second, not the production of heat only as such, but of all other forces correlated with it, which are manifested by the living body.
Foods derived from the animal kingdom are called nitrogenous substances, or azotized. They are also known by the name of proteids. These are mainly derived from meat, milk, eggs, etc. Of several we will examine the chemical composition.
It will be well to state in general terms that all food substances contain in their composition from two-thirds to three-fourths, or even more, of water—some more, some less.
Proteids.
| Albumen. | Caseine. | Syntonin. | Gluten. | Gelatine. | |
| Carbon, | 72 | ||||
| Hydrogen, | 112 | ||||
| Oxygen, | 23 | ||||
| Nitrogen, | 18 | ||||
| Sulphur, | 1 | ||||
| Phosphorus, | R. 2 |
Non-Nitrogenous Substances.
| Carbon. | Hydrogen. | Oxygen. | ||
| 1. | Starch (amyloids), | 18 | 30 | 15 |
| Sugar cane, | 12 | 22 | 11 | |
| 2. | Oils and fats composed of stearic acid of mutton or beef, | 18 | 36 | 2 |
| 3. | Mineral—Saline matters, as chloride of sodium, phosphate of lime. | |||
Animals cannot subsist on any but organic substances, and these must contain the elements which are naturally combined with them—in other words, not even organic compounds are nutritive unless they are supplied in their natural state. Pure fibrine, pure gelatine, and other principles purified from the substances naturally mingled with them, are incapable of supporting life for more than a brief time. Moreover, health cannot be maintained by any number of substances derived exclusively from one only of the two chief groups of elementary principles mentioned above. A mixture of nitrogenous and non-nitrogenous organic substances, together with the inorganic principles which are severally contained in them, is essential to the well-being, and generally even to the existence, of an animal. The truth of this is demonstrated by experiments performed for the purpose; and is also well illustrated by the composition of the food prepared by nature as the exclusive source of nourishment to the young mammals, namely milk. The composition of milk is:
| Human. | Cow’s. | |
| Water, | 890 | 858 |
| Solids, | 110 | 142 |
| 1000 | 1000 | |
| Caseine, | 35 | 68 |
| Butter, | 25 | 38 |
| Sugar (with extracts), | 48 | 30 |
| Salts, | 2 | 6 |
| 110 | 142 |
| Carb. | Hyd. | Nit. | Oxy. | Sulph. | R (unknown). | |
| Caseine, | 72 | 112 | 18 | 23 | 1 | 2 |
In milk, it will be seen from the preceding table, the albuminous group of aliments is represented by the caseine, the oleaginous by the butter, the aqueous by the water, the saccharine by the sugar of milk.
Let us compare the composition of these four organic substances and water:
| Oxy. | Hyd. | Carb. | Nitr. | Sulph. | R (unknown element). | |
| Water, | 1 | 2 | ||||
| Sugar, OH2+ | 11 | 22 | 12 | |||
| Caseine, | 23 | 112 | 72 | 18 | 1 | 2 |
| Olein, | 6 | 38 | 21 |
Among the salts of milk are phosphate of lime, alkaline and other salts, and a trace of iron; so that it may be briefly said to include all the substances which the tissues of a growing animal need for their nutrition and which are required for the production of animal heat.
The yolk and albumen of eggs stand in the same relation as food for the embryos of oviparous animals, that milk does to the young mammalia; and affords another example of mixed food being provided as the most perfect nutrition. The composition of fowl’s egg is:
| White. | Yolk. | ||
| Water, | 80.0 | 53.73 | |
| Albumen, | 15.5 | 17.47 | |
| Mucus, | 4.5 | yellow oil | 28.75 |
| Salts, | 4.0 | 6.0 |
The food substances. 1. Amyloids, starch and sugars. Starch is derived from grain and vegetables, as wheat, barley, rye, oats, corn, rice, sago, tapioca, beans, peas, etc.
The vegetables contain from 75 to 90 per cent of water. Starch and sugars are derived from such as potatoes, turnips, carrots, beets, etc., etc.
The fruits are largely composed of water, sugars, and acids.
All these classes of food contain only three elements.—Starch:
| Carbon. | Hydrogen. | Oxygen. |
| 18 | 30 | 15 |
In their composition we have fifteen molecules of water presented carrying eighteen atoms of carbon. Sugar:
| Carbon. | Hydrogen. | Oxygen. |
| 12 | 22 | 11 |
In this case again we have eleven molecules of water carrying twelve atoms of carbon. This is the chemical composition of starch and sugar food.
2. Fats are also composed of three elements only—carbon, hydrogen, and oxygen. Take the fat of mutton or pork:
| Carbon. | Hydrogen. | Oxygen. |
| 21 | 40 | 1 |
All other animal oils and fats are composed of these three elements only.
3. Albuminous substances—meats, beef, mutton, veal, pork, birds, and fish, of all descriptions.
4. Besides these, mineral salts, already mentioned.
5. And lastly, water—of which by far the greatest quantity is consumed.
The quantity of food ought to be in amount sufficient to replace the waste products of the body. An amount should be taken into the system equal in kind and quantity to the material expended.
Since we know the amount of carbon, hydrogen, nitrogen, oxygen, and the salts that are excreted by the kidneys, skin, and lungs, we may easily calculate the amount of various kinds of food needed to replace them. The outcome being known, the income can be regulated accordingly.
The expenditure or waste, we have seen, in daily loss amounts in carbon to about 4,500 grains, and in nitrogen to 300 grains; besides a certain quantity of water, etc. We therefore require starchy substances, meat and fat, water, etc., to replace the quantity lost. Bread, for example, contains 30 per cent of carbon and 1 per cent of nitrogen. If bread alone, therefore, were taken as food, a man would require in order to obtain the requisite nitrogen 30,000 grains, containing of carbon, 9,000 grains; of nitrogen, 300 grains—an excess of carbon above the amount required of 4,500 grains. But a combination of bread and meat would supply much more economically what was necessary:
| Carbon. | Nitrogen. | |||
| 15,000 grains of bread (rather more than 2 pounds) contains | 4,500 | grs. | 150 | grs. |
| 5,000 grains of meat (about ¾ pounds) contains | 500 | 150 | ||
| 5,000 | 300 | |||
So that ¾ pounds meat and 2 pounds of bread, or its equivalent, would supply the needful carbon and nitrogen with but little waste.
From all these facts it will be plain that a mixed diet is the best and most economical for man; and the result of experience entirely coincides with what might have been anticipated on theoretical grounds only.
The quality and quantity of foods to be taken depends largely upon their digestibility.
The quantity of food necessary for a healthy man taking free exercise in the open air is as follows:
| Meat | 16 | ounces or | 1 | pound avoir. | ||
| Bread and all other carbohydrates, | 19 | ounces,, or,, | 1 | .19 | pound,, avoir.,, | |
| Fat, butter, | 3 | ½ | ounces,, or,, | 0 | .22 | pound,, avoir.,, |
| Water | 52 | ounces,, or,, | 3 | .38 | pound,, avoir.,, |
The quantity and quality of food taken into the system every twenty-four hours, should depend upon the amount and kind of labor done, whether muscular or nervous, whether sitting or not, inactive or active, whether indoors or out of doors; upon the kind of atmosphere we breathe; upon season and climate, etc.; also upon the opportunities we have of throwing off the surplus carbon and nitrogen that the system has been overcrowded with.
These conditions determine the proper variations of the income, since that has to be regulated and corrected by the outcome, and amounts after all to just so much carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus, saline matter, and water as are contained in the proteids, fats, carbohydrates, salts, and water.
It matters little how food is prepared. The main feature is that the supply is equal to the loss, of good and wholesome quality. Whether the food is manipulated by an artistic $10,000 cook or by a plain, clean housewife, the result is the same. Whether the special sense of taste, the gustatory nerve, has or has not undergone a high course of training and education, the fact remains that all that can be supplied is the necessary material that has been expended by the work and labor done by the muscular and nervous tissues.
The subjoined results, selected from Boussingault, exhibit in a tabular form the relative quantity of organic and inorganic constituents in several kinds of herbage compared in several cases with the root or grain. The water was previously driven off by thorough drying:
| Leaves of Mangel-Wurzel. | Root of Mangel-Wurzel. | Potato Tops. | Potatoes. | Pea Straw. | Peas. | Clover Hay. | Wheat Straw. | Wheat. | |
| Carbon | 38.10 | 42.75 | 44.80 | 43.72 | 45.80 | 46.06 | 47.53 | 48.48 | 46.10 |
| Hydrogen | 5.10 | 5.77 | 5.10 | 6.00 | 5.00 | 6.09 | 4.69 | 5.41 | 5.80 |
| Oxygen | 30.80 | 43.58 | 30.50 | 44.88 | 35.57 | 40.53 | 37.96 | 38.79 | 43.40 |
| Nitrogen | 4.50 | 1.66 | 2.30 | 1.50 | 2.31 | 4.18 | 2.06 | 0.35 | 2.27 |
| Ashes | 21.50 | 6.24 | 3.90 | 3.90 | 11.32 | 3.14 | 7.76 | 6.97 | 2.43 |
| 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 |
Subjoined is a table from the same work of the percentage of mineral substances taken up from the soil by various plants:
| Substances Which Yield Ashes. | Acids | Chlorine. | Lime. | Magnesia. | Potash. | Soda. | Silica. | Oxide of Iron, Ammonia etc. | Charcoal, moisture, and loss. | ||
| Carbonic. | Sulphuric. | Phosphoric. | |||||||||
| Potatoes | 13.4 | 7.1 | 11.3 | 2.7 | 1.8 | 5.4 | 51.5 | traces | 5.6 | 0.5 | 0.7 |
| Mangel-Wurzel | 16.1 | 1.6 | 6.1 | 5.2 | 7.0 | 4.4 | 39.0 | 6.0 | 8.0 | 2.5 | 4.2 |
| Turnips | 14.0 | 10.9 | 6.0 | 2.9 | 10.9 | 4.3 | 39.7 | 4.1 | 6.4 | 1.2 | 5.5 |
| Potato Tops | 11.0 | 2.2 | 10.8 | 1.6 | 2.3 | 1.8 | 44.5 | traces | 13.0 | 5.2 | 7.6 |
| Wheat | 0.0 | 1.0 | 47.0 | traces | 2.9 | 15.9 | 29.5 | traces | 1.3 | 0.0 | 2.4 |
| Wheat Straw | 0.0 | 1.0 | 3.1 | 0.5 | 8.5 | 5.0 | 9.2 | 0.3 | 67.6 | 1.0 | 3.7 |
| Oats | 1.7 | 1.0 | 14.9 | 0.5 | 3.7 | 7.7 | 12.9 | 0.0 | 53.3 | 1.3 | 3.0 |
| Oat Straw | 3.2 | 4.1 | 3.0 | 4.7 | 8.3 | 2.8 | 24.5 | 4.4 | 40.0 | 2.1 | 2.9 |
| Clover | 25.0 | 2.5 | 6.3 | 2.6 | 24.6 | 6.3 | 26.6 | 0.5 | 5.3 | 0.3 | 0.0 |
| Pease | 0.5 | 6.7 | 30.1 | 1.1 | 10.1 | 11.9 | 35.3 | 2.5 | 1.5 | traces | 2.3 |
| French Beans | 3.3 | 1.3 | 26.8 | 0.1 | 5.8 | 11.5 | 49.1 | 0.0 | 1.0 | traces | 1.1 |
| Horse Beans | 1.0 | 1.6 | 34.2 | 0.7 | 5.1 | 8.6 | 45.2 | 0.0 | 0.5 | traces | 3.1 |
CHAPTER XIX.
THE ELIMINATION OF WASTE SUBSTANCES.
The expenditures of the human body, or the waste products which arise from the activity of the master tissues, are thrown off by the excretory tissues, as the lungs, the skin, the kidneys, and the terminal part of the intestines.
The lungs are hollow organs, and we may consider them as really two bags containing air, each of which communicates by a separate orifice with a common air tube, through the upper part of which, the larynx, they freely communicate with the external atmosphere. The orifice of the larynx is guarded by muscles, and can be opened or closed at will.
Each lung is partially subdivided into separate portions called lobes. The right lung has three lobes, and the left lung has two. Each of these lobes, again, is composed of a large number of minute parts, called lobules. Each pulmonary lobule may be considered a lung in miniature, consisting as it does of a branch of a bronchial tube, air-cells, blood-vessels, nerves, and lymphatics, with a sparing amount of areolar tissue.
The terminal portion of each lobule is composed of a group of pouches or air-cells, which communicate with the intercellular air passages. These cells are of various forms, according to the mutual pressure to which they are subject. Their cell walls are nearly in contact, and they vary from 1⁄50 to 1⁄90 of an inch in diameter.
Outside the cells a network of pulmonary capillaries is spread out so densely that the interspaces or meshes are even narrower than the vessels, which are on an average 1⁄3000 of an inch in diameter.
Between the atmospheric air in the cells and the blood in the vessels nothing intervenes but the thin membrane of the cells and the capillaries, and the delicate epithelium lining the former. And the exposure of the blood to the air is the more complete because the folds of membrane between contiguous cells, and often the spaces between the walls of the same, contain only a single layer of capillaries, both sides of which are thus at once exposed to the air.
The enlargement of the capacity of the chest in inspiration is a muscular act; the muscles concerned in producing the effect being chiefly the diaphragm, the external intercostal muscles, etc.
From the enlargement produced in inspiration, the chest and lungs return in ordinary tranquil expiration by their elasticity; the force employed by the inspiratory muscles in distending the chest and overcoming the elastic resistance of the lungs and chest wall being returned as an expiratory effort when the muscles are relaxed.
The acts of expansion and of contraction of the chest take up, under ordinary circumstances, a nearly equal time, and can scarcely be said to be separated from each other by an intervening pause. The quantity of air that is changed in the lungs in each act of ordinary tranquil breathing is variable, but probably 30 to 35 cubic inches are a fair average in the case of healthy young and middle-aged men. The total quantity of air which passes into and out of the lungs of an adult, at rest, in 24 hours, has been estimated to be about 686,000 cubic inches. This quantity is largely increased by exertion; and it has been computed that the average amount for a hard-working laborer in the same time is 1,568,390.
Breathing air is the quantity of air which is habitually and almost uniformly changed in each act of breathing.
Complemental air is the quantity of air over and above this which a man can draw into the lungs in the deepest inspiration.
After ordinary expiration, such as that which expels the breathing air, a certain quantity of air remains in the lungs which may be expelled by a forcible and deeper expiration; this is termed reserve air. But even after the most violent expiratory effort, the lungs are not completely emptied; a certain quantity of air remains in them, over which there is no voluntary control, which may be called residual air. Its amount depends, in great measure, on the absolute size of the chest, and has been variously estimated at from 40 to 200 cubic inches.
| Power of Inspiratory Muscles. | Power of Expiratory Muscles. | ||||||
| 1.5 | inches. | weak | 2.0 | inches. | |||
| 2.0 | inches.,, | ordinary | 2.5 | inches.,, | |||
| 2.5 | inches.,, | strong | 3.5 | inches.,, | |||
| 3.5 | inches.,, | very strong | 4.5 | inches.,, | |||
| 4.5 | inches.,, | remarkable | 5.8 | inches.,, | |||
| 5.5 | inches.,, | very remarkable | 7.0 | inches.,, | |||
| 6.0 | inches.,, | extraordinary | 8.5 | inches.,, | |||
| 7.0 | inches.,, | very extraordinary | 10.0 | inches.,, | |||
The blood as it moves through the respiratory organs is exposed to the air that alternately moves into and out of the air-cells and minute bronchial tubes. The blood is propelled from the right ventricle through the pulmonary capillaries in steady streams, and slowly enough to permit every minute portion of it to be for a few seconds exposed to the air, with only the thin walls of the capillary vessels and air-cells intervening.
The atmosphere we breathe has in every situation in which it has been examined in its natural state a nearly uniform composition. It is a mixture of oxygen and nitrogen, carbonic acid, and watery vapor, with traces of other gases, as ammonia, sulphuretta, hydrogen, etc. Of every 100 volumes of pure atmospheric air, 79 volumes consist of nitrogen and 21 of oxygen, about. The proportion of carbonic acid is extremely small: 10,000 volumes of atmospheric air contains only about 4 or 5 of carbonic acid. The average quantity of watery vapor in the atmosphere in this country is about 1.40 per cent.
The changes produced by respiration on the atmosphere are that: 1. It is warmed; 2. Its carbonic acid is increased; 3. Its oxygen is diminished; 4. Its watery vapor is increased; 5. A minute amount of organic matter and of free ammonia is added to it.
1. The expired air is hotter than the inspired air. The temperature varies from 97° to 99½°.
2. Carbonic acid in respired air is always increased; but the quantity exhaled in a given time is subject to change from various circumstances. From every volume of air inspired about 4½ per cent of oxygen is abstracted; while rather a smaller quantity of carbonic acid is added in its place. Under ordinary circumstances, the quantity of carbonic acid exhaled into the air breathed by a healthy adult man amounts to 1,346 inches, or about 636 grains, per hour. It is estimated that the weight of carbon excreted from the lungs is about 173 grains per hour, or rather more than 8 ounces in 24 hours.
Of course the influence of age, sex, respiratory movements, external temperature, season of the year, purity of the respired air, hygrometric state of the atmosphere, period of day, food and drink, exercise and sleep, have to be taken in consideration.
The oxygen of respired air is always less than in the same air before respiration, and its diminution is generally proportionate to the increase of the carbonic acid. It has been shown that for every volume of carbonic acid exhaled into the air 1.17421 volumes of oxygen are absorbed from it; and that when the average quantity of carbonic acid, i.e., 1,346 cubic inches, or 636 grains, is exhaled in the hour, the quantity of oxygen absorbed in the same time is 1,584 cubic inches, or 542 grains.
The nitrogen in the atmosphere, in relation to the respiratory process is supposed to serve only mechanically, by diluting the oxygen, and moderating the action upon the system.
The most obvious change which the blood undergoes in its passage through the lungs is that of color, the dark venous blood being exchanged for the bright scarlet arterial blood. It gains oxygen, loses carbonic acid, becomes 1° to 2° F. warmer; it coagulates sooner and more firmly, and contains more fibrine.
The venous blood as it issues from the right ventricle is loaded with carbonic acid. The oxygen present is insufficient to the whole of the hæmoglobin of the red corpuscles; much reduced hæmoglobin is present, hence the purple color of venous blood. As the blood-vessels pass through the capillaries of the lungs, this reduced hæmoglobin takes from the pulmonary air its complement of oxygen, all or nearly all the hæmoglobin of the red corpuscles becomes oxy-hæmoglobin, and the purple color forthwith shifts into scarlet. The hæmoglobin of arterial blood is saturated or nearly saturated with oxygen. Passing from the left ventricle to the capillaries, some of the oxy-hæmoglobin gives up its oxygen to the tissues, becomes reduced hæmoglobin, and the blood in consequence becomes once more venous, with a purple hue. Thus the red corpuscles by virtue of their hæmoglobin are emphatically oxygen-carriers. Undergoing no intrinsic change in itself, the hæmoglobin combines in the lungs with oxygen, which it carries to the tissues; these, more greedy of the oxygen than itself, rob it of its charge, and the reduced hæmoglobin hurries back to the lung in venous blood for another portion. Hæmoglobin combines loosely with carbonic oxide just as it does with oxygen, but the affinity with the former is greater than with the latter. While carbonic oxide readily turns out oxygen, oxygen cannot so readily turn out carbonic acid. This property of carbonic oxide explains its poisonous nature.
Respiratory changes in the tissues. Arterial blood passing through the several tissues, becomes once more venous. A considerable quantity of the oxy-hæmoglobin becomes reduced, and a quantity of carbonic acid passes from the tissue into the blood. The blood which comes from a contracting muscle, is not only richer in carbonic acid, but also, though not to a corresponding amount, poorer in oxygen, than the blood which flows from a muscle at rest.
A muscle is always producing carbonic acid, and when it contracts there is a sudden and extensive increase of the normal production. Oxygen is necessary for the life of the muscle. When venous blood instead of arterial blood is sent through the blood-vessel of a muscle, the irritability speedily disappears, and unless fresh oxygen be administered the muscle soon dies.
Our knowledge of the respiratory changes in muscle is more complete than in the case of any other tissue; but we have no reason to suppose the phenomena of muscle are exceptional. On the contrary, all the available evidence goes to show that in all the tissues the oxidation takes place in the tissues and not in the adjoining blood. It is a remarkable fact, that lymph, serous fluid, bile, urine, and the other secretions contain no free or loosely combined oxygen, while the tension of carbonic acid in peritoneal fluid is as high as six per cent, and in bile and urine is still higher, etc.
All these facts point to the conclusion, that it is the tissues, and not the blood, which become primarily loaded with carbonic acid, the latter simply receiving the gas from the former by diffusion; and that the oxygen which passes from the blood into the tissues is at once taken up in the same combinations, so that it is no longer removable by diminished tension.
The production of carbonic acid in the muscle is not directly dependent on the consumption of oxygen. The muscles produce carbonic acid in an atmosphere of hydrogen. What is true of muscle is true also of other tissues and of the body at large.
Oxygen helps to wind up the vital clock; but once wound up, the clock will go on for a period without further winding (Pflüger).
To sum up, then, the result of respiration in its chemical aspect. As the blood passes through the lungs, the low oxygen tension of the venous blood permits the entrance of oxygen from the air of the pulmonary alveolus, through the thin alveolar wall, through the thin capillary sheath, through the thin layer of blood plasma, to the red corpuscles, and the reduced hæmoglobin of the venous blood becomes wholly, or all but wholly, oxy-hæmoglobin. Hurried to the tissues, the oxygen, at a comparatively high tension in the arterial blood, passes largely into the tissues, in which the oxygen tension is always kept at an exceedingly low pitch, by the fact that the tissues, in some way at present unknown to us, pack away, at every moment, into some stable combination each molecule of oxygen which they receive from the blood. With much, but not all, of its oxy-hæmoglobin reduced, the blood passes on as venous blood. How much hæmoglobin is reduced will depend on the activity of the tissue itself. The quantity of hæmoglobin in the blood is the measure of limit of the oxidizing power of the body at large; but within that limit the amount of oxidation is determined by the tissue, and by the tissue alone.
The skin is an excretory tissue, and consists principally of two layers, an external covering of epithelium, termed the cuticle or epidermis, and a layer of vascular tissue, named the corium derma or cutis vera. The integument serves (1) for the protection of deeper tissues, (2) as a sensitive organ in the exercise of touch, (3) as an excretory organ, (4) as an absorbing organ, (5) for regulating the temperature of the body. Within and beneath the corium are imbedded several organs with special functions, namely, sudoriferous or sweat glands, sebaceous or fat glands, and hair follicles; and on its surface are sensitive papillæ. The so-called appendages of the skin, the hair and nails, are modifications of the epidermis.
Sudoriferous glands: In the middle of each of the transverse furrows between the papillæ, and irregularly scattered between the bases of the papillæ in those parts of the surface of the body in which there are no furrows between them, are the orifices or ducts of the sudoriferous, or sweat glands, by which it is probable that a large portion of the aqueous and gaseous materials excreted by the skin are separated. Each of these glands consists of a small lobular mass, which appears formed of a coil of tubular gland-duct surrounded by blood-vessels and imbedded in the subcutaneous adipose tissue. From this mass the duct ascends, for a short distance, in a spiral manner through the deeper parts of the cutis, then passing straight, and then sometimes again becoming spiral, it runs through the cuticle and opens by an oblique, valve-like apparatus. The sudoriferous glands are abundantly distributed over the whole surface of the body; but are especially numerous, as well as very large, in the skin of the palm of the hand. They are estimated from 2,738 to 3,528 in each superficial square inch. They are almost equally abundant and large in the skin of the sole. The glands by which the peculiar odorous matter of the axilla is secreted form a nearly complete layer under the cutis, and are like the ordinary sudoriferous glands, except in being larger and having very short ducts. In the neck and back, where they are least numerous, the glands amount to 417 on the square inch. The total number is estimated, at 2,381,248; and supposing the orifice of each gland to present a surface of 1⁄54 of a line in diameter (and regarding a line as equal to 1⁄10 of an inch) the whole of the glands would present an evaporating surface of about eight square inches.
Sebaceous glands secrete a peculiar fatty matter. Like the sudoriferous glands, they are abundantly distributed over most parts of the body.
The quantity of matter which leaves the human body by way of the skin is very considerable. It is estimated that while 7 grains pass through the lungs per minute, as much as 11 escape through the skin. The amount varies extremely. It is calculated that the total amount of perspiration excreted from the whole body in 24 hours might range from 2 to 20 kilos.
The total amount of perspiration is affected not only by the condition of the atmosphere, but also by the nature and quantity of food taken, the amount of fluid drunk, and the amount of exercise taken. It is also influenced by the mental condition, by medicines and poisons, by disease, and by the relative activity of the other excreting organs, more particularly the kidneys.
The fluid perspiration or sweat, when collected, is found to be a clear colorless fluid, with a strong and distinctive odor varying according to the part of the body from which it is taken. Besides accidental epidermic scales, it contains no structural elements. Its reaction is generally acid, but in cases of excessive secretion may become alkaline. The average amount of solids is about 1.81 per cent, of which about two-thirds consists of organic substances. The chief normal constituents are (1) sodium chloride (common salt), with small quantities of other inorganic salts; (2) various acids of the fatty series, such as fermic, acetic, butyric acid, with probably other acids—CH2O2-C2H4O2—C4H8O2; (3) neutral fats and cholestrine; (4) ammonia (NH3) (urea), and possibly other nitrogenous substances.
The average loss by cutaneous and pulmonary exhalation in a minute is from 17 to 18 grains; the minimum, 11 grains; the maximum, 32 grains; of the average 18 grains 11 pass by the skin and 7 by the lungs. The maximum loss by exhalation, cutaneous and pulmonary, in twenty-four hours is about 3¾ pounds; the minimum, about 1½ pounds. Valentine found the whole quantity lost by exhalation from the respiratory and cutaneous surfaces of a healthy man who consumed daily 40,000 grains of food and drink to be 19,000 grains, or 2½ pounds. Subtracting from this, for the pulmonary exhalation, 5,000 grains, and for the excess of the weight of the exhaled carbonic acid over that of the equal volume of the inspired oxygen, 2,256 grains, the remainder, 11,744 grains, or nearly 15⁄7 pounds, may represent an average amount of cutaneous exhalation in a day.
The Kidneys, two in number, are excretory organs. They are deeply seated in the lumbar region, one on each side of the vertebral column, at the back of the abdominal cavity, and behind the peritoneum. The kidneys measure about 4 inches in length, 2½ inches in breadth, and 1½ inches in thickness. The left is usually longer and narrower than the right one. The weight of the kidney is usually stated to be about 4½ ounces in the male and somewhat less in the female.
The excretory apparatus consists of fine tubules (the tubuli urineferi), malpighian bodies, blood-vessels, nerves, and lymphatics, etc.
The kidneys are highly vascular, and receive their blood from the renal arteries, which are very large in proportion to the organ they supply. Each artery breaks up into four or five branches, these again subdivide and break up into capillaries in the substance of the kidney. The veins arise by numerous venous radicals from the capillary network of the kidney, as seen near the surface of the gland, and collect the blood from the capillary plexus around the convoluted tubules which mainly compose this part, the smaller veins joining together and ultimately forming a single vein and ending in the inferior vena cava.
The kidneys are so arranged by their anatomical structure—that of the cortical and medullary substance, the tubuli urineferi, pyramids, malpighian bodies, etc.—that they separate from the blood the solids in a state of solution. The secretion takes place by the agency of the gland cells, and equally in all the parts of the urine tubes. The protoplasmic cells which line at least a large portion of the tubuli urineferi elaborate from the blood certain substances, and discharge them into the channels of the tubules. All parts of the tubular system of the kidney take part in the secretion of urine as a whole, but there is another provision of vessels for a more simple draining off of the water from the blood when required.
The large size of the renal arteries and veins permits so rapid a transit of the blood through the kidneys that the whole of the blood is purified by them. The secretion of urine is rapid in comparison with other secretions, and as each portion is secreted, it propels that which is already in the tubes onwards into the pelvis of the kidney. Thence, through the ureter, the urine passes into the bladder, into which its rate and mode of entrance has been watched. The urine does not enter the bladder at any regular rate, nor is there a synchronism in its movement through the two ureters. In a recumbent posture the urine collects for a little time in the ureters, then flows gently, and if the body is raised, runs from them in a stream till they are empty. Its flow is increased in deep inspiration, or straining, and in active exercise, and in fifteen or twenty minutes after meals.
Substances taken into the stomach pass very rapidly through the circulation. It does not take longer than one minute for ferrocyanide of potassium to pass through. Vegetable substances pass in from sixteen to thirty-five. Neutral alkaline salts with vegetable acids, which were generally decomposed in transitu, made the urine alkaline in twenty-eight to forty-seven minutes. But the time of passage varied much; and the transit was always slow when the substances were taken during digestion.
There are really two distinct parts in the kidney—the actively secreting part, the epithelium of the secreting tubules; and what maybe called a filtering part, the malpighian bodies.
The specific gravity of urine is 1020—that is, the average human urine. Urine varies—in the morning before breakfast it is darker, urina sanguinis; urine secreted shortly after the introduction of any considerable quantity of fluid into the body, urina potus; and the urine evacuated immediately succeeding a solid meal of food, urina cibi. The last kind contains a larger quantity of solid matter than either of the others, the first and second being largely diluted with water.
Specific gravity: The morning urine is best calculated for analysis. The average healthy range may be stated at 1015 in the winter to 1025 in the summer, and variations of diet and exercise may make a great difference. In disease, the variations may be greater; sometimes descending in albuminaria to 1004, and frequently ascending in diabetes, when the urine is loaded with sugar, to 1050, or even to 1060.
The whole quantity of urine secreted in twenty-four hours is subject to variations according to the amount of fluid drunk, and the proportion of the latter passing off from skin, lungs, and alimentary canal. The average quantity voided in twenty-four hours by healthy male adults from twenty to forty years of age amounts to 52½ fluid ounces.
The chemical composition of urine. The average quantity of each constituent of the urine in 1,000 parts is:
| Water (O H2), | 967 | ||||
| Urea (C O N2 H4), | 14 | .239 | |||
| Uric acid (C5 N4 H4 O3), | .468 | ||||
| Coloring matter, mucus, and animal extractive matter, | 10 | .107 | |||
| Salts. |  | Sulphates (soda, potash), |  | 8 | .185 |
| Bisulphates (lime, soda, magnesia, ammonia), | |||||
| Chlorides (sodium, potassium), | |||||
| Silica, etc., | Traces. | ||||
| 1,000 | .000 | ||||
Urea is the principal solid constituent of the urine, forming nearly one-half of the whole quantity of solid matter. It is also the most important ingredient, since it is the chief substance by which the nitrogen of decomposed tissue and superfluous food is excreted from the body.
The salts excreted by the kidneys in 24 hours are:
| Urea (C N2 H4 O), | 512 | grains. | |
| Chloride of sodium (Na Cl), | 177 | grains.,, | |
| Phosphoric acid (H3 P O4), | 48 | grains.,, | |
| Sulphuric acid (H2 S O4), | 31 | .11 | grains.,, |
| Uric acid (C5 N4 H4 O3), | 8 | .53 | grains.,, |
The substances excreted consist mainly of carbonic acid gas (C O2), which is expired by the lungs, and urea (C N2 H4 O), which is expelled by the urine.
These excretions, or expenditures, or waste products of the human body, present the carbohydrates—starch, sugars, and fats—and the proteids—meats and albumen—taken into the system as food.
The daily average loss by the expenditure or waste products of the body is estimated to be about:
| Carbon, | 4,500 | grains. |
| Nitrogen, | 3 to 500 | grains. |
| Besides salts and water. |
Of all the elements of the income and outcome, the nitrogen, the carbon, and the free oxygen of respiration, are by far the most important. Since water is of use to the body for merely mechanical purposes, and not as food in the strict sense of the word, the hydrogen element becomes a dubious one; the sulphur of the proteids, and phosphorus of the fats, are insignificant in amount; while the saline matters stand on a wholly different footing from the other parts of the food, inasmuch as they are not sources of energy, and pass through the body with comparatively little change.
The correct income will consist of so much nitrogen, carbon, hydrogen, oxygen, sulphur, phosphorus, saline matters, and water, contained in the proteids, fats, carbohydrates, salts, and water of the food, together with the oxygen absorbed by the lungs, skin, and alimentary canal.
The outcome will consist of: 1. The respiratory products of the lungs, skin, and alimentary canal, consisting chiefly of carbonic acid and water, with small quantities of hydrogen and carburetted hydrogen, these two latter coming exclusively from the alimentary canal; 2. Perspiration, consisting chiefly of water and salts, with urea by the skin, and other organic constituents of sweat amounting to very little; 3. The urine, which contains practically all the nitrogen really excreted by the body, as well as a large quantity of saline matter and water.