"Whence do they derive it? In whatever way they obtain the nitrogen, man may also acquire it, although he should never taste flesh;-provided his organization be adapted for assimilating food of a vegetable nature: which has been already proved. Now, in herbivorous animals, there appears to be only five possible sources of azote:-1. The vegetables upon which they feed. 2. The air swallowed with the food. 3. The converting powers of the secretions of the various viscera; as the stomach, liver, pancreas, &c. 4. The azote resulting from the decomposed tissues being again organized. 5. The atmosphere, by means of the process of respiration.

179. If we admit the conclusion of former chemists, that vegetables contain little or no nitrogen, then, whatever portion of this element the flesh of herbivorous animals contains, we must evidently refer to one or more of the four remaining sources; and to which ever of these we attribute it, we are bound to admit that man has equal facilities for obtaining it, even if confined to a vegetable diet. Let us first inquire, then, what light physiology throws upon the subject; and then proceed with an examination of the proximate and ultimate principles of vegetables.

180. The Herbivora swallow much more air with their food, than the Carnivora; and Despretz has ascertained, by experiment, that the former expire more nitrogen than the latter;—a fact which is inexplicable unless we admit, that nitrogen can be supplied in larger quantities than the food itself contains. The Carnivora never masticate their food; but the Herbivora and man have teeth adapted

to this purpose; by which means the food becomes intimately mixed with the saliva, which (Liebeg says) possesses the property of enclosing air in the shape of froth, in a far higher degree than even soap-suds. "This air", he observes, "by means of the saliva, reaches the stomach with the food; and there its oxygen enters into combination; while its nitrogen is given out through the skin and lungs, without being applied to any use in the animal economy." This last observation of Liebig seems to me supported by no evidence; nor can I for one moment admit, that nature would allow nitrogen to be incessantly passing through the various tissues of the body, by means of the stomach and lungs, without answering some useful purpose. It is possible, therefore, that additional nitrogen may be supplied to the system, by means of mastication and insalivation, when the food does not contain a sufficient quantity. Dr. Prout remarks-"This involution of azote may be considered as one of the great objects of mastication and insalivation, which are almost peculiar to animals chiefly subsisting on saccharine matters."

181. Chemists generally take it for granted, that food is the only means by which azote can be added to the blood; and that the animal body has no power to convert the non-azotized elements of foods into azotized compounds. Certain physiologists, however, are of a different opinion; and believe, that there may take place many changes and conversions in the mysterious vital laboratory of an animal, which cannot be imitated in the unorganized laboratory of the chemist. It is probable, that all organic structures have the power of reducing

nutrient substances to the simple elements; and of recomposing them, by means of affinities controlled by the vital agency. It is not impossible, even, that during the vital process some of the ultimate principles may be both decomposed and generated. This appears to be the opinion of Dr. Prout; who observes-"My belief is that, under certain extraordinary circumstances, the vital agents can form what we now consider as elements; but that, in ordinary, such elements are chiefly derived ab externo, in conjunction with the alimentary principles." Again: he states that, "under extraordinary circumstances, the assimilating organs may be able to decompose principles which are still considered as elementary; nay, to form azote or carbon."

182. "It is therefore much more safe and philosophically accurate", says Sylvester Graham, "for chemists to say what inorganic forms or kinds of matter result from a chemical analysis of organic substances, than it is for them to state that organic substances are composed of such and such chemical elements, or kinds of matter. We know, it is true, that all material bodies are composed of that common matter of the world, which modern chemistry has distributed into more than fifty elements; and we know that, in manufacturing its various organic substances out of that common matter, the vital economy employs more of some of those elements than of others. We also know, that some of those elements, or forms of matter, are much better adapted to the purposes of the living body than others; but we have no right to assume, that the vital forces possess no higher energies

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of analysis, than are exerted by the chemical agents of the inorganic world; nor that their principles of combination, in any respect, resemble those of inorganic chemistry. On the contrary, we have reason to believe, that vitality decomposes all those substances used in its economy, which chemists call 'elements; and that, in arranging its various organic substances and structures, its synthetical operations are very different from those of inorganic chemistry. It is therefore purely hypothetical to assert, that oxygen and carbon and hydrogen and azote, and other chemical elements (as such) combine, in the vital processes, to form the various substances and structures of the organic system.” *

183. It is well known that the vegetable, being supplied with ammonia, can form gluten out of what would otherwise have been deposited as starch; and Dr. Prout has distinctly stated, that he has found albumen (an azotized principle) in the duodenum, when none was found in the stomach: from which circumstance he concludes, that a highly azotized substance may be secreted from the blood, either in the stomach or duodenum or both, for the purpose of being united with the non-azotized constituents of the food, to form a compound adapted to the nutrition of the tissues. He also supposes, that the portion of blood thus deprived of its azote, is separated from the general mass of blood by the liver, as one of the constituents of the bile; which secretion, as a whole, is remarkably deficient in azote.

* GRAHAM'S LECTURES ON THE SCIENCE OF HUMAN LIFE. Vol. 1. P. 81.

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184. Tiedemann and Gmelin, as well as other physiologists, believe that the secretion of the pancreas adds to the chyme richly azotized animal substances, albumen, casein, and osmazome; by which it is brought nearer to the chemical composition of the blood, and prepared for its complete assimilation to it. Thus is a portion of nitrogen supplied to such alimentary matter as was originally destitute of it. Hence the large size of the pancreas, and the more copious secretion of the pancreatic fluid, in herbivorous than carnivorous animals; hence the change that is said to be produced in the size of this organ, by a long continued change in the habits of an animal; hence, also, its smaller size in the wild cat, which lives only on animal food, than in the domestic cat, which lives partly on animal and partly on vegetable food. It would seem, therefore, that the pancreas is a compensating organ; the function of which is to maintain a due balance of protein in the chyle, into which the chyme of the stomach is converted in the duodenum: and it is not improbable, that the spleen exercises a similar office for the chyle, in its further progress. Müller thinks it probable, that the spleen secretes lymph of a peculiar nature; which, being mixed with the contents of the lymphatic and lacteal system coming from other parts, tends to perfect the formation of the chyle. A large amount of fat, and a small quantity of fibrin, are found in the lacteals previously to their passing through the glands of the mesentery, and to their receiving the lymph from the spleen; after which the proportions are reversed. It appears, therefore, that the oleaginous principles of food,