The reader will, however, hardly be sur prised when he is informed, that these condi tions have never yet been fulfilled; and hence, that a satisfactory account of this interesting fluid reinains at present impossible. But he must not therefore think the above allusions superfluous. For it is only by a reference to these conditions of experiment, that we can judge how far we ought to accept the state ments made by various recent observers re specting this fluid.
Thus Frerichs* obtained intestinal juice from fasting cats and dogs, in whom a few inches of intestine had been emptied, and tied at both ends, about five hours before they were killed. Lehmann t procured it from a fistula of the small intestine, which had fol lowed an operation for hernia in the human subject ; and in which another fistula, higher up, gave passage to the ordinary mixed con tents of this part of the alimentary canal. Zander instituted fistulm in animals. And, finally, Bidder § and Schmidt, who adopted Frerichs' method without obtaining one drop of intestinal juice, carefully compared the mix ture withdrawn from simple fistulw, with a very small quantity of a purer fluid which was yielded by clogs in whom the pancreatic and biliary ducts had been tied, and the gall bladder made to discharge its contents externally.
According to all these observers, the intestinal juice is a transparent, viscid, and strongly alkaline fluid. It contains nuclei, and round or columnar nucleated cells ;— an abortive cell-growth, the admixture of which does not substantially affect the struc tureless character of the secretion. Of its composition and reactions we can only say, that it appears to contain mucus and the ordinary salts; which together form a solid residuum, that amounts to about 2 per cent. of the whole quantity of fluid.* As regards the physiological properties of the intestinal juice, it has the power of con verting starch into grape sugar. But however obvious the usefulness of this capacity, it is possessed in an equal degree by so many other animal substances, that it can hardly be re garded as the specific purpose or function of this secretion.f But the recent observations of Zander, together with those of Bidder and Schmidt, claim for this secretion a much more impor tant office :— an office which would entitle the whole of the small intestine to that ap pellation of a " ventriculus succenturiatus," which was formerly bestowed on the duode num. These observers agree in the state ment, that the intestinal juice dissolves protein compounds, both in and out of the body. And from the careful quantitative researches of Bidder and Schmidt, it would follow, not only that its solvent powers upon these sub stances are from three to four times greater than those of the gastric juice itself, but that in the Dog, about half the daily albumen of a flesh diet is habitually left untouched by the stomach, to undergo solution in the intestine by the secretion.
Against such a conclusion would suggest the following arguments, which together in duce me to think that this doctrine ought not at present to be accepted. That a large organ like the stomach, with a definite and com plicated structure, should so incompletely discharge its single chemical function, is a paradox which alone involves a great improba bility. This suspicion becomes still stronger %hen we consider that, under normal circum stances, gastric juice is always conveyed f'rom the stomach into the intestine during the pro cess of gastric digestion ; while it is evident that none of the experiments by these observers quite exclude the possibility of such a transit. Nay more, if we suppose—what is surely not impossible — that the juice carried onwards into the intestine is there concentrated by the partial absorption of its watery part, some of the strange quantitative results obtained by Bidder and Schmidt cease to be altogether in explicable. It may indeed be urged, that the alkaline character observed in the inlestinal juice sufficiently proves that its digestive pro perties are not derived from the stomach. But although the addition of a caustic alkali destroys the efficiency of gastric juice, still such a process seems very different from that absorption of acid, or that gradual admixture of a dilute alkaline solution, by which a similar reaction would probably be communicated in the living intestine. And, finally, is it like the ordinary economy of Nature, that an elaborate secretion should pass the pylorus, to be at once annihilated, and then replaced by a second and equally complex antagonist juice ? On such a supposition, indeed, there are many animals in whom almost all the gastric juice would be wasted. For example, there is great reason to suppose that the sojourn of food in the Horse's stomach is so brief, that anything like the stomach digestion of Carnivora is impossible. But are we therefore entitled to assert that this org,an is utterly useless? Such considerations appear to render it more probable, that the gastric juice may retain its digestive efficacy after passing through the pylorus ; and that the presence of this secretion in the small intestine suffi ciently explains the solvent powers of the juice which is found in this situation.