82 PHYSIOLOGY. 



psychic effect dies out. If meat has been eaten, the secretory center- 

 will still be strongly excited in a reflex manner from the stomach and 

 intestine, while, at the same time, the trophic center receives only 

 weak impulses from the peripheral terminations of the nerves in ques- 

 tion. When bread is eaten the reverse happens. After the cessa- 

 tion of the psychical stimulus, the secretory fibers are now only weakly 

 excited through the end-apparatus; the trophic, on the other hand, 

 are strongly influenced. In the case of fat foods reflex inhibitory 

 impulses proceed to the centers which affect the activity of both secre- 

 tory and trophic nerves. 



ACTION OF AGENTS ON THE STOMACH. 



When absolute alcohol or a strong emulsion of oil of mustard was 

 introduced in the small stomach (Pawlow), there was an enormous 

 secretion of mucus. 



Ice-cold water in the large stomach (Pawlow) causes the secre- 

 tion, which is subsequently produced by an ordinary meal, to be less 

 than normal, more especially in the first hour; here is a special 

 inhibitory reflex. 



W T hen alcohol is poured into the large stomach (Pawlow) an 

 extremely free secretion of gastric juice begins in the small stomach 

 (Pawlow). The secretion in the small stomach was compensatory 

 for the arrested secretion in the large stomach. 



In hypersecretion of the stomachs of dogs he found sodium bicar- 

 bonate to have a good effect. In hyposecretion he found water a 

 good agent. 



Borrisow has shown that bitter substances, such as gentian, excite 

 the flow of gastric juice. 



Hydrochloric acid, when secreted in considerable quantity, pre- 

 vents further secretion of gastric juice. Phosphoric acid does not 

 inhibit. Butyric acid strongly excites gastric secretion. 



ACTION OF THE GASTRIC JUICE. 



The amylolytic action of the saliva, the conversion of starch into 

 maltose, is dependent upon the presence of ptyalin, an organic fer- 

 ment whose action is best carried on in a neutral or alkaline medium. 

 The proteolytic action of the gastric juice is due to the presence of its 

 organic ferment, or enzyme, pepsin, in an acid medium. A par- 

 tial digestion of certain foodstuffs can be accomplished in an acid 

 solution, if given sufficient time and the proper temperature. There 

 is, however, a strong tendency toward putrefaction during the pro- 



