STOMACH AND INTESTINE.— (Syn. Stomach, formerly Maw, Eng. ; Mogen, Germ.; aTokaxoc, yacriip, Gr.; Stomachus, Ventriculus, Lat. ; Stomaco, Ventricolo, Ital. ; Estomac, Fr.; E stontaco, Sp. ; — Intestine or bowel, formerly gut, tripe, entrail, Eng.; Dann., Germ.; rzmpov, Gr. ; Intestinum, Lat.; inicstino, Ital. Sp.; Intestin, Fr. it) What are calied the organs of the animal body consist of a diversity of tissues, so grouped and united with each other as to tbrm a more or less continuous and aggregate mass ;—the functions of these various struc tures being also associated in a single general purpose, which may, be regarded as the sum of their several actions on the system at large.
Among such groups of structures, there is none more. remarkable than that which effectuates the series of processes collectively termed DIGESTION. For other organs are so far exclusively dependent on the blood, as that many influences of the outer world can scarcely reach them, except through the medium of this fluid. Entrenched, as it were, behind this the great river of ani mal life, they are secured from any but the indirect action of numerous physical agents. But the organ of digestion lies out side this stream : and occupies a kind of neutral territory, betvveen life and matter, where the various forces of both can co operate for its benefit, in equal and har monious conjunction. Or rather, let us say, the digestive canal is the threshold of the House of Life, where dead matter is first endowed with those properties which enable it to become a living constituent of the animal body.
The group of organs before us has indeed a special relation to the animal. For although digestion is usually enumerated amongst those general or organic functions which are shared in by everything that has life,—vege table as well as animal,—still the means by which the process is effected in these two forms of organization, constitute as important a distinction between them, as the mere pre sence or absence of other functions. So that, the digestive cavitv is, on the whole, as charac teristic of the animal, as the organs of loco motion and innervation of which it is the exclusive possessor.
How far the so-called vegetative functions are really alike, or even comparable to each other, in the two kingdoms of nature, it is not our object here to inquire. As little do we wish to introduce, what some might perhaps think less out of place, a detailed comparison between the digestive functions of the plant and animal. But as the cavity which it is our express object to describe is all but univer sally present in the latter, and absent from the former organization, it seems desirable briefly to contrast them in this respect.
In th e animal, a highly azotized composition is connected with,—and probably essential to,— an active life; which, in its turn, implies a rapid waste of substance. On the other hand, the plant lives slowly, wastes little, and contains but a small quantity of azotized material.
The food of each appears to correspond vvith these requirements. That of the plant is, in great part, inorganic ; consisting mainly of compounds which pervade the soil that surrounds its roots, or the air which bathes its leaves. While that of the anitnal is or
ganic :--i. e. the substances which compose it are the products of a previous organization.
The elaboration of the food repeats the preceding contrast. The plant builds up in organic into organic matter ;— a process of chemical synthesis, which may well be effected with great difficulty, and by slow stages. While theanimal scarcely does more than convert one proximate principle into another ;—a meta morphosis which involves no change of com position, and the facility of which is but par tially counterbalanced by its requisite rapid ity and amount, and the delicacy of its ad justment.
The agents of these processes are also susceptible of comparison. For in the vege table they appear to be closely- connected with various external forces, such as light and heat; while in the animal they seem more inherent to the organism.* And in both, the site of the elaboration or change in the food corresponds to those situa tions where the above agents are inost readily applicable in the plant, to the leaves and other green parts of its surface; in the animal, to a cavity in its interior. The pre sence of such a cavity not only permits the less frequent application of n utritions substance to be compensated by the ingestion of large quantities at particular times ; but, while it thus meets the peculiar requirements of an animal organism, also allows of that loco motion which is so necessary to the mere prehension and selection of its scarcer food. Its subjection to volition renders ingestion a work of rapid and powerful mechanical force, in place of a slow physical imbibition. And finally, the same internal situation which directly subjects its contents to the agents of the digestive metamorphosis, also isolates them from all surrounding objects, besides favouring the temperature often necessary to the operation.t The reader will, however, observe, that the title of the following article does not announce an essay on the process of digestion, or the various organs w hich effect it; but limits itself to two portions of the alimentary canal, hitherto undescribed in this work. But it is impossible to treat of the functions of the stomach and intestine except in connection with the entire process in which they take so large a share. While the numerous observa tions and researches which have been made since the appearance of the earlier article DioEsTios require some notice in the Supplement of which the present essay forms a part. For these reasons the author has felt it advisable not to confine himself too strictly to the exact limits w hich the heading " Sto ntach and Intestine" might seem to imply. Hence, though the following essay will treat chiefly of the above segments of the alimentary canal, it will also comprise a very brief account of whatever is at present known concerning the whole tligestive act. Commencing by a rough sketch of the anatomy of these parts in the animal kingdom, we shall successively consider, their structure and functions in the human sobject ; their relation to digestion and nutri tion ; and finally, their appearances in disease.