trypsinogen is converted into trypsin, it has the power of destroying the 

 secretin. Moreover, as I mentioned in my last lecture, such a localised 

 formation and excretion of an antibody has no analogue among the facts 

 hitherto brought to light by bacteriologists as to the formation of anti- 

 bodies in general. We are inclined to think that the action of secretin is 

 that of a specific drug that just as pilocarpin acts on all the glands of 

 the body, including the pancreas, so secretin acts on the pancreas with, 

 perhaps, one or two other glands which are associated with the pancreas- 

 in their functions. Its action is not, however, identical with that of 

 pilocarpin. The latter drug induces in the pancreas the secretion of a 

 thick viscid juice containing from 7 to 8 per cent, of solids. Its action is 

 entirely abolished by the injection of a small dose of atropin. On the 

 other hand, secretin produces a juice containing about 3 per cent, of 

 solids, which resembles in every particular the juice obtained from an> 

 animal with a pancreatic fistula after it has received food. Its action is 

 not altered in any way by the previous injection of, at any rate, moderate 

 doses of atropin. 



The discovery of a chemical reflex, which is sufficient to explain 

 the correlation of activities between the mucous membrane of the small 

 intestine and the pancreas, must cause us to inquire how far these results 

 are to be reconciled with the previous results obtained by Pawlow. 

 According to Pawlow's original idea the reflex secretion of pancreatic 

 juice was entirely nervous. The question now arises whether both 

 mechanisms function in normal circumstances or whether it is possible 

 to explain all Pawlow's results by the chemical mechanism which I have 

 described. Although we cannot at the present time give a definite answer 

 to this question, we are inclined to believe that the chemical mechanism 

 is the only one involved in the secretion of pancreatic juice, and that in 

 all Pawlow's experiments, where secretion was excited by the stimulation 

 of nerves such as the vagus or splanchnics, the effect on the pancreas was 

 really a secondary one, due to movements of the stomach arising as a 

 result of the nerve stimulation, and squeezing some of its acid contents 

 into the first part of the small intestine. Other workers, however, such 

 as Fleig and Wertheimer, believe that both mechanisms are at work 

 namely, that through the mucous membrane of the intestine the pancreas 

 can be excited to secrete by both nervous and chemical means. We 

 ourselves have never been able by nervous means to obtain secretion of 

 pancreatic juice, provided that we excluded all possibility of entry of acid 

 into the upper part of the small intestine. 



The discovery of this simple chemical nexus between alimentary canal 

 and pancreas suggests at once the possibility of other mechanisms of the 

 same description taking part in the complex chain of events involved in 

 the digestion of our foodstuffs. Investigations on this point, carried out 

 partly in my laboratory and partly by independent observers, have shown 

 this belief to be justified, and I propose in my third lecture to deal with 

 the facts at present ascertained which point to a whole chain of such 

 chemical reflexes throughout the alimentary tract. 



