128 THE WORK OF THE DIGESTIVE GLANDS. 



brought all their real constituents under consideration. We must 

 naturally have a knowledge of all of these and determine their import- 

 ance. It is from the effects of the elementary constituents that each 

 separate point of the curve of secretion which we observe after a com- 

 plex meal, must be explained. In order to solve this problem we must 

 successively combine the individual constituents with each other, must 

 synthetically build up the food step by step, and, moreover, must submit 

 the properties of the juice at each phase to an exact analysis. In the 

 case of a complex food we shall then be in a position to draw con- 

 clusions from the properties of the juice as to what is the effective 

 excitant. Thus from the degree of alkalinity of the pancreatic juice 

 one could decide whether its secretion was caused by acids or not. A 

 correspondence in the results obtained by both methods the analytic 

 and the synthetic furnishes the best assurance of their reliability. 



The systematic investigation of the elements of the food must 

 undoubtedly lead to the discovery of many unexpected relationships 

 between the food-stuffs on the one hand and the digestive glands on 

 the other. A complete answer to the two groups of questions, why 

 and in what way gland activity varies, will only be obtained when an 

 exact investigation of the contents of the digestive canal is joined hand 

 in hand with observations upon secretory activity ; when, for instance, 

 for any given period of digestion, and for every point of the digestive 

 canal, we know precisely where a certain constituent of the food 

 is to be found, and what alterations it is at that moment being sub- 

 jected to. The latter group of questions concern, on the one hand, 

 the effects of the elementary food constituents, that is to say, their seat 

 of action, their mode of working, and the combined results of the local 

 specific excitants. On the other hand, they deal with the chain of 

 phenomena in the central nervous system, determined not only by 

 peripheral impulses from the digestive canal, but also by impulses from 

 other organs as well. The questions in these two groups are, of course, 

 interwoven in the closest manner. It is probable that the same 

 questions likewise apply to those digestive fluids, such as the bile and 

 the succus entericus, which have not as yet found place within the limits 

 of our subject, because their physiology, from the point of view of these 

 lectures, has not been sufficiently worked out. Recent experiments of 

 Dr. Bruno, carried out in the laboratory upon the entry of bile into 

 the intestine, have shown quite as exact and intimate a connection 

 between this event and the nature of different sorts of food as we have 

 already learned for the gastric and pancreatic juice. Although much 

 more remains to be done, we have reason to be satisfied with what has been 

 accomplished. Our results, I hope, have at once and for ever done away 

 with the crude and fruitless idea that the alimentary canal is universally 



