234 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 reexcreted 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 pan- 

 creatic 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 reexcreted 

 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 tinder the name of zymogen, given to it by Heidenhain, but 

 the writer heard it described by Kiihne 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 di- 

 gesting in very dilute acid and then neutralizing or alkalizing ; there 

 seeming to exist a ferment-forming substance in the pancreas." Dur- 

 ing 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 circu- 

 late throughout the tissues without doing them any injury. 



Whether this be the case or not, however, with regard to the fer- 

 ments 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 un- 

 dergo 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 



