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Page:Popular Science Monthly Volume 18.djvu/246

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THE POPULAR SCIENCE MONTHLY.

little doubt. It has been demonstrated in the case of the bile, which is absorbed with great rapidity from the intestine and reëxcreted by the liver, so that it does not pass into the general circulation at all. But what becomes of the other digestive fluids, and the ferments they contain? The pepsin finds it way in minute quantities through the liver, and has been discovered in various tissues of the body and in the urine. This, however, matters but little, for it can not act upon the tissues themselves, inasmuch as they possess an alkaline reaction. But the case must be somewhat different with pancreatine, and if pancreatic fluid be absorbed from the intestine and pass through the liver unchanged, we should expect that it would have a very powerful action upon the tissues throughout the body, because there appears to be no reason why it should not act upon them just as it does upon the food in the intestine itself. It seems not at all unlikely, then, that the liver has got another function besides those usually assigned to it, viz., that of preventing the digestive ferments from reaching the general circulation so as to act upon the tissues. Now, we do find in the liver itself and in the bile a ferment having the same diastatic power as the pancreatic juice, but it does not appear in such quantities as one would expect if the whole of the pancreatic ferment were simply reëxcreted by the liver along with the bile, and, as we have no evidence that the ferment is destroyed during its action in the intestine, we are naturally led to think that it may undergo a change in the liver, the converse of that which it undergoes in the pancreatic gland during the process of secretion. In the pancreas itself we have no ready formed ferment, but we have a ferment-forming substance, which has recently become known under the name of zymogen, given to it by Heidenhain, but the writer heard it described by Kühne in his lectures on physiological chemistry delivered at Amsterdam in 1869. I quote verbatim from the notes which I took at the time of his lecture on the pancreas: "Glands which have no action on fibrine can be made active by digesting in very dilute acid and then neutralizing or alkalizing; there seeming to exist a ferment-forming substance in the pancreas." During digestion this ferment-forming substance or zymogen splits up and yields free ferment, and it seems not improbable that it is in the liver that this very ferment, after its digestive work is done, becomes again converted into the ferment-forming substance which may circulate throughout the tissues without doing them any injury.

Whether this be the case or not, however, with regard to the ferments of the gastric, pancreatic, and intestinal juices, all of which must pass through the liver before they reach the general circulation, there can be no doubt that the products of intestinal digestion do undergo very marked changes indeed in the liver, as is shown by the formation from them of very large quantities of a new substance, glycogen—a substance which is not contained in the products of the gastric and intestinal digestion which reach the liver, and yet which