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while the carnivora (or flesh-eating tribes) obtain it indirectly from the blood and flesh of the herbivorous animals upon which they prey.
These remarks naturally lead us to a proper consideration of those substances which form chiefly the food of those animals which are bred, reared, and supported by the farmer either for agricultural labor or as food for man, and in many cases for both. Strange to say, they are principally herbivorous in their nature. Examine chemically, therefore, any article which they consume—no matter whether it is wheat, beans, peas, cabbage, carrots, or turnips-we shall soon find that, besides water, it has gum, sugar, starch, and a considerable quantity of woody fibre, in union with a small portion of a fatty matter; all these constituents, as I observed in my former lectures, will be found to be composed only of three elements, viz: oxygen, carbon, and hydrogen, which exist combined in nearly the same proportions. But we likewise find that there are many other substances contained in vegetables which contain nitrogen; and this is in addition to those elements which compose starch, gum, &c., and are known to the chemist by the appellations of gluten, vegetable albumen, and casein. Now, if we take a small quantity of fine wheaten flour, mix it with water into a paste, and well wash it upon a sieve, by pouring a stream of cold water over it while it is kneaded with the hand, all the sugar, starch, and gum will pass away through the sieve with the water, and the substance left behind will resemble bird lime, being of an equally tenacious nature; this is, therefore, the gluten which the wheat contained, and when dried, the water which it possessed being evaporated, it resembles horn, being a hard, brittle mass; and if burnt, it emits a similar unpleasant effluvia to burnt horn, feathers, or other animal matter. The gluten which is obtained from peas, beans, or the fibrin and vegetable albumen procured from the expressed juices of the carrot, turnip, or cabbage, all possess analogous properties to those found in wheat, with this exception, that they are all soluble in cold water; whereas the gluten which is obtained from wheat is not. If we submit these substances to the test of chemical analysis, we speedily discover them to be all composed of the same constituents, and also that they are likewise identically the same as those composing the flesh and blood of animals generally; but you must please to bear in mind that this remarkable identity does not consist in their containing azote or nitrogen, in combination with oxygen, carbon, and hydrogen, in the same, or nearly the same, proportions as in animal flesh and blood; but it extends to the existence of a small quantity of sulphur and phospho. rus, which is found to be associated with the muscular flesh, forming one of the soft tissues of the animal. Hence we may very properly assert, as a physiological axiom, that the flesh and blood are, by the great Author of Nature, found actually ready prepared and elaborated in the vegetable. The plant it is which elaborates and duly prepares all the
ents of water, carbonic acid, and ammonia, which constituent particles are found to be identically the same as the muscular animal flesh; consequently the animal has nothing more to do than to apply them to his own use for the purposes of nutrition, secretion, and the vivification of life.
The following table, adopted by my talented friend, Professor Gyde, of Painswick, will give the reader an idea of the actual identity of com position existing between these substances:
Every animal body momentarily undergoes some physiological change; every motion, thought, and action is of course performed at the expense of some, and many of almost every, part of the body. These incessant alterations and action cause the great demand for food which nature constantly requires to repair the waste that is continually taking place. You may speedily ascertain the truth of this fact by noticing its illustration in those animals which have long been kept without food, or had but a scanty supply, or where it did not possess sufficient nutritious properties; and also in those animals which have undergone great exertion and bodily fatigue, when contrasted with those but little fatigued, and whose food was good in quality and sufficient in quantity. The fine horses formerly attached to our well-appointed coaches, before the construction of railroads and the employment of giant steam power, and which vehicles will ere long only be remembered by being recorded in the pages of history, among the phenomena that have been and are passed away—the fine horses I have named were almost exclusively fed upon oats and beans, which are two of the most nutritious kinds of all species of vegetable food; while, on the other hand, those horses performing but a small amount of laborious work will supply the natural waste of their bodies from the very small comparative quantity of gluten which is to be contained in hay or clover, or both.
I have already informed you that the food of all classes of animals con sists of two kinds of distinct species of matter, viz: the one which possesses a great proportion of azote or nitrogen as one of its principal constituents, and which the table 1 have referred to tells us is identified with the blood and muscular flesh of the animal. The other portion is destitute of nitrogen, but consists of gum, starch, sugar, and woody fibre. Now, every one of these different materials answers two quite distinct, but very important purposes in the economy of the animal body. The first, or the nitrogenous constituents, supply the waste which has occurred in the fluids and tissues of the body, and, as Dr. Magendie very properly states, may justly be termed the elements of nutrition. The last, which are the nonnitrogenous portion, act, if I may apply the expression, as fuel for combustion in the lungs, in order to keep up the due supply of animal heat, and, under some peculiar circumstances, also, will contribute to the formation of fat. These elements may likewise be arranged under two great heads, viz: those which are necessary to the function of nutrition, and those affecting that of respiration.
I respectfully call your attention to the following table, wherein they are exemplified:
1. Elements of nutrition.
2. Elements of respiration.
The elements of nutrition (No. 1) must of necessity exist in combination with every substance which experience has taught us to be capable of supplying food to the animal; but, ere it can impart the nutritious properties, numerous important mechanical and chemical changes must take place. The grand process of digestion must be performed, by which I mean the manner by which the nutrient particles may be rendered soluble, and not only capable of entering, but even of forming new blood. A brief detail of the manner in which this is performed may not be uninteresting to some of my present auditory. It is aecomplished in the following manner: the food, when received into the mouth, is broken down by the teeth, where it becomes mixed with the saliva which is secreted by the glands that are situated near the angle of the jaw, and beneath the tongue; when the process of mastication is completed, the morsel is collected into a ball at the base of the tongue, and by the act of deglutition, or swallowing, it is carried past the pharynx into the æsophagus, or gullet, down which it passes into the stomach, where it enters at the cardiac orifice; it remains there for a short time, according to the nature both of the animal and the food it has partaken of (in man it is supposed to be about two hours). The chemical and mechanical action that now takes place is technically called, in physiological language, the process of chymification; when this is perfected, the orifice at the opposite extremity (denominated the pylorus) becomes dilated, and the chyme passes into the first of the small intestines, anatomically named the duodenum, where it becomes mixed with the bile from the liver and the fluid from the pancreas, or sweet bread. This being accomplished, the process of chylification now commences: a series of small, minute vessels, named lacteals, whose mouths open on the mucous (or villous) coat of the bowel, or intestine, absorb the nutritious portion of the food (which resembles milk in appearance; hence it is. named chyle). This fluid, being conducted by numerous branches, passes into one great reservoir, called the thoracic duct, which ends in a large vein near the heart, (the left subclavian,) and there it is mixed with the blood; but being loaded with carbon, which is inimical to the due preservation of human life, the blood passes from the heart to the lungs, where it becomes oxygenized, and fit for all the purposes of the animal economy. The non-nutritious portion, from which the chyle has been
. extracted, passes through the last of the small intestines (ihe jejunum) into the whole course of the larger part of the alimentary canal, viz: the cocum, colon, and rectum; and from the last they are finally ejected from the body, ultimately again to re-enter it in another form, in consequence
of its forming manure, and therefore affording food for plants, in the manner detailed in my former lectures.
But independent of the simple fact, that the salivary fluid, when commixed with the food, renders the digestion of the aliment far more easy, yet Baron Liebig imagines that it possesses the peculiar offices of enclosing and combining air in the form of froth; the oxygen which it contains enters into union with the constituents of the food, while the nitrogen is again evolved through the medium of the lungs and skin. This philosopher is likewise of opinion that, in many of the herbivorous quadrupeds, their rumination (as the oxen and sheep, for ex. ample) has for one of its principal objects a complete renewal with the repeated introduction of pure oxygen into the animal's stomach; and that, unless this takes place, the function of rumination cannot be duly perfected in the stomach. I have given you a brief outline of the manner in which digestion is accomplished; but in doing so I omitted to observe that, attached to the mucous or villous coat of the stomach, are a series of minute glands, which secrete what is denominated the gastric juice, or fluid, and which, among other matters, contains a quantity of pure mucus, in combination with a small quantity of free hydrochloric or muriatic acid, (called, in common language, spirits of salts,) with a peculiar principle known to chemists under the appellation of pepsin, and which has been confirmed by Dr. Sylvester, of Clapham, to be, in itself, a most active and virulent poison, but whose noxious properties are chemically neutralized in the stomach and intestines during the function of digestion.
I have stated that hydrochloric acid is always present in the stomach, and particularly so during the digestive process. For the discovery of this curious but important chemical fact, we are indebted equally to M. Tiedman Gmelin, of Germany, and Dr. Prout, of London. This acid may be artificially obtained by the decomposition of chloride of sodium, or common table salt (which is only a combination of pure muriatic acid and soda). The acid is of great service in promoting the function of digestion in the stomach, while the soda, as an alkali, copiously enters into the formation of bile. Thus it is that a certain proportion of salt is necessary to digestion in every species of animals—at least as far as our knowledge extends in the classes of quadrupeds and birds; and although chemistry tells us that it is an essential ingredient in the burnt ashes of the vegetables, yet we very rarely find it existing in a sufficient quantity to form a regular supply of either in the acid or soda which is required for the due performance of the function of healthy digestion; and, there. fore, not only should we ourselves partake of a certain quantity daily with our own food, but should place some within the reach of both birds and cattle under our management in the farms we are connected with. Nature is the philosopher's best monitor, and the scientific farmer cannot do better than to obey her axioms. We find that all classes of animals have, if I may use the expression, an instinctive love for salt, and seek for it as for a portion of their diurnal food. It is well known that the pigeon tribe of birds, if they cannot obtain it elsewhere, will even have recourse to the mortar which cements the bricks of houses together. They have been frequently known to fly to the sea coast in order to procure it; and pigeon-fanciers who are not so honest as to mind borrowing their neighbors' birds will allure them by means of what is known as a salt-cake, placed in or near the dove-cote, wherein muriate of soda forms an essential ingredient. This nefarious practice is now forbidden, very properly, by an act of Parliament, which awards a punishment of seven years' transportation upon conviction. It, however, confirms the important physiological fact I have just noticed.
In the ruminating tribe of the class mammalia, as the ox and the sheep, the important process of digestion differs but little from that which I have stated, and their stomachs are of the simplest construction, being little else than a mere membraneous bag; but in the ruminantia we find their stomachs considerably more complicated, in order that they may be enabled to extract the due proportion of nourishment which they require from the food which they eat; as in the case of grass, by way of example, which we find by chemical investigation contains but very little nourishment in proportion to the bulk. Let us now philosophize for a moment, and see the manner in which the ox and those of his class perform the functions of mastication and digestion. In these creatures the grass is cropped from the surface of the earth by means of the fore teeth, and, after being but very slightly masticated, is swallowed. This process continues uniil the first stomach is filled,* when the animal lies down apparently well and perfectly contented; but it is now that the curious process of rumination commences. In the first stomach the food is mixed with a secreted fluid not dissimilar to the saliva, and in a kind of semi pulpy mass it is returned into the mouth, in small detached portions, where perfect mastication takes place, and during this process the animal is in a recumbent position; after the second and perfect mastication is completed, the food passes into the second stomach, denominated by comparative anatomists omasum; from this it passes into the third stomach, the abomasum; in these last two it undergoes very important changes, and whence it passes into the fourth or really true stomach. It is in this last portion of the curious but complicated species of apparatus that the function of digestion is ultimately and perfectly performed; and the last processes of extracting the nutriment from the food are exactly similar to that which I have described as occurring in man and those animals having simple membraneous stomachs. The vital fluid of all animals is commonly denominated the blood, in which, as Holy
Writ truly observes, “is life;" this fluid is either formed from vegetables, -as in the herbivora, or from flesh, as in the carnivora; yet in both tribes of animals the composition and essential constituents are the same, both in their physical effects upon the system and as portrayed by chemical analysis. We find it circulating throughout not only the principal organs in the living animal, but by means of vessels as fine as the human hair; so extremely delicate are they that they will not admit the thicker coloring particles of the blood itself; yet the properties which the blood possesses are most surprising; it replenishes the fluids and solids which are diminished by the waste, wear, and tear of the body; it places osseous or bony matter in the skeleton for its growth and support; forms fleshy fibres for soft muscular tissue, by which the motions of the body are performed; and from the blood are all the different bodily secretions which are necessary for the healthy existence of the animal secreted and performed; the
* We should here observe that the lecturer exhibited drawings of the stomach, as found in both tribes of animals.--Ed. Plough.