SCIENTIFIC TRACTS

AND

FAMILY LYCEUM.

JANUARY 15, 1834.

[Furnished for the Scientific Tracts and Family Lyceum.] ANALOGIES OF VEGETABLE AND ANIMAL LIFE.

BY EDWARD JARVIS, M. D.

EXAMINING carefully the internal structure of the perfect animal and the perfect vegetable, and observing minutely the manner in which both are fed and nourished, we find a very striking resemblance between the organs of digestion, circulation and respiration of both; for they display the most remarkable property of organized beings, as distinguishing them from dead inorganized matterthat of internal nutrition and growth. They receive into themselves foreign and dead substances, and change them within their own organs to different substances; throw off from themselves such as are not needed for the support of the being, and expose the rest to the air, or breathe upon it, and then from this select one portion for supplying the waste of the body, another for the growth, forming out of it all the varying substances which enter into the man or the tree.

This is but the faint outline; the resemblance will be the more strikingly observable when we shall trace out the minute details, which it will be interesting to follow, and see how nature operates by general laws; for it seems to be her delight, when she has one principle that answers a good purpose, to apply it to as many cases as possible; and in the seemingly almost infinite variety of individuals in her creation, we find comparatively few variations of internal character. But it is not to be supposed that I

take it upon myself to show that the stomach of the animal corresponds exactly to a stomach in a tree: I only mean to prove that the tree digests, or rather changes the character of its food as well as the man; that in both cases the food is, before it is consumed by the tree or animal, a dead kind of matter, entirely different from any matter within the tree or animal; and afterward this is altered in its properties and becomes nutritious sap (succus proprius) in the one case, and blood in the other, and in both is ready to be made a part of the living body; and that in one case this operation is carried on in the stomach and alimentary canal and the ducts leading from the latter to the heart; and in the others it is performed in a set of vessels which lead from the roots to the leaves, answering, anatomically, to the vessels that absorb the chyle from the alimentary canal and carry it to the heart, and corresponding in function to the whole digestive apparatus.

Now, perhaps we may be laughed at as a visionary, with more imagination than rigid observation, if we say there is a stomach, or even an alimentary canal in the bush; but seeing that these changes are effected, which we must call digestion, it will not be too much to say, the tree has a digestive apparatus.

Granting, then, that there is not an exact similarity of organs, we shall find no difficulty in showing that they perform strictly similar operations, whatever may be the organs with which they work.

ANIMAL DIGESTION.

To give a proper idea of this process, as well as to fulfil our purpose of comparing the digestion of both animal and vegetable, it will be first necessary to take a slight view of the stomach and alimentary canal, and the lymphatic sys

tem.

The mouth is the beginning of the digestive organs, and opens into the stomach by the gullet, which is a long tube, lying immediately behind the windpipe and in front of the back bone. The stomach is a long hollow sack, lying across the body just below the breast bone, and underneath the short ribs. Through an aperture near the

left extremity it receives the food from the gullet, and at the other end, after it has digested it, discharges the chyme into the duodenum, which is the first of the bowels.

The alimentary canal varies in length in different animals, according to their different habits of life and kind of food, and the rest of their anatomical structure. In man it is about five times the length of his body-from thirty to thirty-five feet; in animals which live upon vegetables entirely, the ox, horse, sheep, &c., the proportion is longer; and in beasts of prey, whose whole food is flesh, it is shorter; for in the former a longer time is necessary for digestion of vegetables, and consequently this matter must be the longer retained subject to the action of the digestive apparatus; but in the latter, this is sooner accomplished, and therefore both the digestive process and its apparatus is the shorter.

The whole of this canal is lined with what is called the mucous coat, which is thick, soft, loose, and, in the lower bowels, thrown into folds. Those who have eaten tripe, will recollect the honey-comb surface of this excellent article of diet, and the reddish stringy fibres beneath this and the layer of fatty substance which forms the other surface. This is a good example of the stomach and its coats, which any one can see and examine for himself, and then will not forget its character; and we recommend any one who would know the curious workmanship of the human stomach to examine a piece of tripe; to see, first, the mucous membrane, with its complicated folds, which throw out the gastric juice; next, the muscular coat, which performs the motions and carries the food onward; and lastly, the serous coat, which is on the outside, and gives the whole organ its firmness and strength. This arrangement of the coats is nearly the same throughout the alimentary tube, from the gullet downwards; but the mucous membrane of the large intestines is thrown into more distinct folds than in the stomach.

We take our food at particular periods, and sufficient in a few moments to satisfy our appetite and wants for some hours. We take it, when we are hungry, and of our own will. This action is voluntary, and the interval is long. Our food is necessarily broken up in the mouth by the ac

tion of the teeth, rolled over by the tongue, and mixed with the saliva of the mouth, and then is swallowed through the gullet to the stomach. This mechanical division of the aliment, and the mixture with the secretions of the mouth and gullet, seems to be a necessary step in the work of digestion, and preparatory for the second step, which takes place in the stomach: so that writers on the diseases of the stomach attribute the aggravation, at least, if not the just cause of many of these, to the neglect of mastication of the food, and the crude mass being thrown upon the stomach, which is unable readily to do the proper work of the teeth in addition to its own. Hence it will be a matter of safe precaution for our readers to be careful not to swallow their food, before the mouth and teeth have faithfully discharged their duty upon it. The process of swallowing is curious in itself, and still more so as a manifestation of skill and design in the Former of our bodies. To give a full knowledge of it will involve more anatomical description than enters within the scope of this Tract; for we only wish to explain such parts as bear some general analogy to the vegetable processes; and this will be understood when we come to speak of the motion of the food in the bowels.

We have before stated that the inner lining of the stomach throws out the gastric juice, which is a powerful solvent for the food in this organ: by means of this, the aliment is soon reduced to a soft pulpy mass called chyme; its physical and chemical properties are both changed; it has neither the same external character, nor, on analysis, has it the same properties which belonged to the food before it was eaten.

Dr. Philip tried very many experiments on rabbits, to ascertain the particular mode in which digestion is carried on. He found that the food, when newly received into the stomach, was in a somewhat solid mass in the left and large extremity of the stomach: the gastric juice was thrown out from the surface, and mixed with the outer portion of the food, and soon this portion is reduced to chyme, soft and pulpy. Then the constant vermicular motions of the muscular coat carried this digested substance towards the left end of the organ, when it passed

through what is called the pyloric orifice into the first of the small intestines.

It is worth while to notice, in passing, the admirable contrivance of this orifice: at this place the calibre of the stomach is contracted to about the size of a finger. The fibres of the muscular coat are thickened here, and a strong belt of them surrounds this end, creating a narrow neck; and when contracted, this band closes entirely this end, and in states of ordinary health, obstinately keeps it closed, except when the digested food offers itself for passage; then, as if by a sort of intelligence, this faithful sentinel relaxes its hold, the mouth opens, the chyme passes through, but when the unchanged food offers, it closes until this is prepared like its predecessor. This finishes the second stage of digestion; and next comes the third stage, which takes place on the chyme, in the small portions of the alimentary canal.

We have now the food in the duodenum, the first of the small intestines, in the state of chyme. The next process is, to form chyle from this. This is done by aid of the bile which is sent in through a small tube, opening into this bowel from the liver; and still farther help is received from the pancreatic juice, which is made in the pancreas, a gland in the abdomen. What the precise nature of the effect of these liquids is, is not known; and physiologists have exhausted their ingenuity to discover, and their imaginations to invent ways, by which nature receives help from these organs; and, as if nature only meant to provoke our inquiries to show the narrow limits of all our knowledge and to baffle our vain hopes, all the painful experiments of the physiologists, all the laborious investigations of the chemist, and the unwearied observations of the philosophers, have fallen short of their expectations, and left them all in the dark, for they have not brought the

secret out.

They have told us the chemical constitution of gastric juice, of bile, and of the secretions of the pancreas; we know how much carbon, oxygen, nitrogen and hydrogen these contain, and in what proportions they are combined together we are equally learned on the character of chyle, and of the food from which the chyle is formed, on the