DIGESTION AND ABSORPTION IN THE STOMACH. 711 



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 secretin, 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 * 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 substances by the general term of hormones (from 6/y/*w, 

 arouse or excite). 



The researches of Pawlow and his co-workers seem also to in- 

 dicate that the quantity and properties of the secretion vary with 

 the character of the food. The quantity of the secretion varies, 

 also, other conditions being the same, with the amount of food to 

 be digested. The apparatus is adjusted in this respect to work 

 economically. Different kinds of food produce secretions varying 

 not only as regards quantity but also in their acidity and diges- 

 tive action. The secretion produced by bread, though less in 

 quantity than that caused by meat, possesses a greater digestive 

 action. On a given diet the secretion assumes certain characteris- 

 tics, and Pawlow is convinced that further work will disclose the fact 

 that the secretion of the stomach is not caused normally by general 

 stimuli all affecting it alike, but by specific stimuli contained in the 

 food or produced during digestion, whose action is of such a kind 

 as to arouse reflexly the secretion best adapted to the food ingested. 



One of the curves, showing the effect of a mixed diet (milk, 600 

 c.c.; meat, 100 gms.; bread, 100 gms.) upon the gastric secretion, 

 as determined by Pawlow's method, is reproduced in Fig. 271. It will 

 be noticed that the secretion began shortly after the ingestion of the 

 food (seven minutes), and increased rapidly to a maximum that was 

 reached in two hours. After the second hour the flow decreased 

 rapidly and nearly uniformly to about the tenth hour. The acidity 

 rose slightly between the first ancl second hours, and then fell gradu- 

 ally. The digestive power showed an increase between the second 

 and third hours. 



Nature and Properties of Pepsin. Pepsin is a typical proteo- 



lytic enzyme that exhibits the striking peculiarity of acting only in 



acid media; hence peptic digestion in the stomach is the result of 



the combined action of pepsin and hydrochloric acid. Pepsin is 



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



