78 THE ACTIVE FORCES OF LIVING ORGANISMS 



The con- 

 catenation 

 of auto- 

 matic 

 actions 

 and reac- 

 tions in 

 digestion. 



Secretion in the various portions of the digestive 

 system appears to be connected in a certain measure 

 with the chemical nature of the substances present in 

 it. Thus, when the food, rendered slightly alkaline 

 in the mouth by the saliva, descends to the stomach 

 it causes a flow of acid, and it is a well-known fact 

 that this effect can be increased by the use of weak 

 alkalies. The acid acting on the carbohydrates of 

 the food dextrinizes them, and dextrin has been called 

 a peptogen because it augments the secretion of pepsin, 

 an effect which, it is said, is still further increased 

 through the presence of meat. The acidified food in 

 turn, as it passes into the duodenum, acts as a natural 

 excitant to the flow of the alkaline bile, which, mixing 

 with the food, leads to further secretion in the glands 

 of the remainder of the intestinal canal. Throughout 

 the whole of the digestive tract there is, therefore, a 

 concatenation of action and reaction due to chemical 

 transformations in which differences of electrical, 

 potential, and variations of ethereal tension are pre- 

 sumably, as elsewhere, a not unimportant factor. 

 These facts lead to the conclusion that all the pro- 

 cesses of metabolism, including those of digestion, are 

 of an essentially electro-chemical nature. 



The next step which it is necessary to take is to 

 consider the relations existing between metabolism 

 and the nervous system, and to discover, if possible, 

 to what extent the force generated in the electro- 

 chemical processes acts upon the nerve centres and 

 in what degree the latter react. 



