776 PHYSIOLOGY OF DIGESTION AND SECRETION. 



bread and white of eggs, have no effect of this kind at all. If 

 introduced into the stomach of a dog through a fistula so as not to 

 arouse a psychical secretion, for instance, while the dog's attention 

 is diverted or while he is sleeping, they cause no flow of gastric 

 juice and are not digested. If such articles of food are eaten, 

 however, they cause a psychical secretion, and when this has acted 

 upon the foods some products of their digestion in turn become 

 capable of arousing a further flow of gastric juice. The steps in 

 the mechanism of secretion are, therefore, three: (1) The psychical 

 secretion; (2) the secretion from secretogogues contained in the 

 food; (3) the secretion from secretogogues contained in the prod- 

 ucts of digestion. The manner in which the secretogogues act 

 cannot be stated positively. Since the gastric glands possess 

 secretory nerve fibers the first explanation to suggest itself is 

 that the secretogogues by acting on sensory fibers in the gastric 

 mucous membrane reflexly stimulate the secretory fibers. This 

 explanation, however, is rendered untenable by the fact that the 

 effect of these substances is obtained after complete severance 

 of the nervous connections of the stomach. If, therefore, this 

 so-called chemical secretion is produced by a nervous reflex, the 

 nerve centers concerned must lie in the stomach itself, the reflex 

 must take place through the intrinsic ganglion cells. Another 

 more probable explanation has been offered. Edkins * has shown 

 that decoctions of the pyloric mucous membrane, made by boiling 

 in water, acid or peptone solutions, when injected into the blood 

 cause a marked secretion of gastric juice. These substances when 

 injected alone into the blood cause no such effect, and decoctions 

 of the mucous membrane of the fundic end of the stomach are 

 without action on the gastric secretion. This author suggests, 

 therefore, that the secretogogues, whether preformed in the food or 

 formed during digestion, act upon the pyloric mucous membrane 

 and form a substance which he designates as gastrin or gastric se- 

 cretin, and this substance after absorption into the blood is carried 

 to the gastric glands and stimulates them to secretion. The effect 

 is, therefore, not a usual nervous reflex, but an instance of the 

 stimulation of one organ by chemical products formed in another. 

 Starling f has emphasized the fact that this mode of control is 

 frequently employed in the body, as will be described in the 

 following pages in connection with the pancreatic secretion and 

 the internal secretions. He proposes to designate such sub- 

 stances by the general term of hormones (from 6p/jtaco, arouse 

 or excite). Leaving aside for the moment the way in which 

 the secretogogues excite the secretion it is important to empha- 



* Edkins, "Journal of Physiology," 1906, xxxiv., p. 133. 



t Starling, "Recent Advances in the Physiology of Digestion," 1906. 



