families have to the analogous substances which they receive as food from the air and the soil. Agency of decompos com There is, probably, no fact more firmly established, as to its chemical signification, than this, that the ing animal chief constituents of the animal body, albumen, pounds. fibrine, the gelatinous tissues, and caseous matter, when their elements are in a state of motion, that is, of separation, exert on all substances which serve as food for men and animals, a defined action, the visible sign of which is a chemical alteration of the substance brought in contact with them. ations de pending on the pre sence of ferments. That the elements of sugar, of sugar of milk, of Transformstarch, &c., in contact with the sulphurised and nitrogenised constituents of the body, or with the analogous compounds which occur in plants, when these are in a state of decomposition, are subjected to a new arrangement, and that new products are formed from them, most of which cannot be produced by chemical affinities, this is a fact, independent of all theory. Chemical affinities exert an influence on the nature of the new products, but do not determine their formation. The cause of this is obvious. When an organic substance is decomposed by a chemically active body, we can, in most cases, predict the nature and the properties of the new products formed by its action. If the active chemical agent be an acid, all, or a part of, the elements of the organic body combine to form a base, or to form water; if it be a base, they unite to form an acid, that is, a compound, the properties of which Agency of compared ordinary affinity. ferments with that of The trans formation caused by a ferment varies with the state of the ferment. in the vital are opposed to those of the acting body, and by which, therefore, its affinity is neutralised. In the processes called fermentation and putrefaction, the mode of arrangement of the elements of organic compounds is of a totally different kind; because here it is not a foreign chemical attraction, but another cause, which determines the new arrangement. Now we know, with absolute certainty, that the products which may be generated from fermentescible substances vary, as the state of the ferment or exciter varies. The same caseine, the same membrane, which determine the transposition of the elements of sugar so as to form lactic acid, cause, in another state, the same elements to divide themselves into carbonic acid and alcohol, or into butyric acid, carbonic acid, and hydrogen gas. These prinNo one can fail to perceive the significance of ciples are concerned these facts, in respect to the understanding and the processes. explanation of many of the vital processes. If a change in the position and arrangement of the elementary molecules of animal compounds can exert, out of the body, a decided influence on a number of organic substances, when brought in contact with them; if these substances are thus decomposed, and new compounds formed of their elements; and if we consider, that among these compounds, namely, such as are susceptible of fermentation, are included all those matters which constitute the food of man and of animals, it cannot be doubted, that the same cause plays a most important part in the vital pro cess; that it has a great share in the alterations which nutritious matters suffer when they are converted into fat, into blood, or into the constituents of organised tissues. We know, indeed, that in all parts of the living animal body a change takes place; that portions of living tissues are separated; that their constituents, Fibrine, Albumen, Gelatine, or whatever they may be called, give rise to new compounds; that their elements combine to form new products; and in the present state of our knowledge we must suppose that, by means of this very action, at all points where it occurs, according to its direction and force, a parallel, or corresponding, change is effected in the nature and composition of all the constituents of the blood or of the food which come into contact with them; and that, consequently, the change of matter is itself a chief a chief cause of the transformations which the constituents transformof the food undergo, and also a condition of the process of nutrition. We must further admit, that with every modification produced by a cause of disease in the process of transformation of an organ, of a gland, or of one of their constituents, the action of this organ on the blood conveyed to it, or on the nature of the resulting secretion, must, in like manner, be changed; that the effect of a number of remedies depends on the share which they take in the change of matter; and that such remedies exert an influence on the quality of the blood or of the food, chiefly in this way, that they alter the direc The change of matter is cause of the ations of the food. The change influenced of matter is by diseases and by re medies. Relation of urea, uric the food, very little known. tion and force of the action taking place in the organ, which action they may accelerate, retard, or arrest. The intermediate members of the almost infinite seacid, &c. to ries of compounds which must connect Urea and Uric acid with the constituents of the food, are, with the exception of a few products derived from the bile, almost entirely unknown to us; and yet each individual member of this series, considered by itself, inasmuch as it subserves certain vital purposes, must be of the utmost importance in regard to the explanation of the vital processes, or of the action of remedies. The chief constituent of bile is a crystallisable compound; and no physiologist now denies, that it is indispensable for the process of digestion. The arrangements found in the body must have reference to the vital processes. Were we to discover in the organism certain arrangements by which a permanent electrical current must be determined at all points, could any one doubt that such a current must take a share in the vital processes? Or if it were proved, that from the constituents of the food of all animals, among other compounds, organic bases are formed, which in their chemical nature resemble caffeine or quinine, or any other organic base; if such compounds could be detected everywhere, in all parts, or only in certain parts, of the organism, should we not have advanced a step nearer to the explanation of the action of caffeine or of quinine? About ten years since, the ultimate analysis of organic bodies furnished physiology with a result deductions composi fibrine, al bumen, and caseine. highly important, in order to the easy understand- Erroneous ing of the digestive or nutritive process, by demon- from the supposed strating, that fibrine, albumen, and caseine have the identity in same composition. Misled by this result, many che- tion of mists thought that the chief problem to be solved by chemistry was to ascertain, by ultimate analysis, the composition, in 100 parts, of all the constituents of the body; and thus many were induced to act on each of these constituents, without a more minute study of its chemical relations and its properties, with alcohol, ether, and acids; and with the aid of the known resources of organic analysis, to determine the percentage of carbon, nitrogen, hydrogen, and oxygen. They believed that they had thus, by means of these numerical results, done a real service to physiology, although the only addition thus made to the name of the substance analysed was an empty formula, of the accuracy of which there was no evidence whatever. Now that No prowe have been for ten years in possession of these been made formulæ, every one must perceive that we have of mere made no real progress. The cause of this is obvious to all who know the true value of ultimate analysis. Ultimate analysis is a means of acquiring knowledge, but is not itself that knowledge. Even supposing, what no one will seriously maintain with regard to the constituents of the animal body, that analysis had made us acquainted with the exact proportions in which their elements are united together, yet this knowledge gives us not the least in gress has by the aid formulæ. |