188 



DIGESTION 



by the sight, taste, smell, or even thought of food when the individual 

 is hungry to some extent. For experimental purposes gastric juice is 

 usually obtained from dogs in which a gastric fistula opening outward 

 on the belly has been established. Sometimes an esophageal fistula 

 opening on the exterior is also made and so arranged that food passes at 

 the will of the observer either into the stomach or directly outside the 

 body. To obtain a supply of gastric juice it is only necessary, then, to 

 give the animal in this way a fictitious meal, whereupon reflex neural 

 impulses cause a copious flow of the desired liquid, which is removed 

 through the gastric fistula. 



FIQ. 90 



Fio. 91 



Two sorts of glands found in the gastric mucosa. 



DIGESTION IN THE STOMACH is brought about chiefly by three 

 enzymes or ferments pepsin, rennin, and lipase and by the hydrochloric 

 acid. The action of the pytalin, too, secreted in the mouth, occurs also 

 for the most part in the gastric fundus. We will next briefly examine 

 into the chemical changes produced in various classes of foods by these 

 still mysterious agents. 



Ptyalin appears to have been first isolated from saliva by Mialke and 

 in a somewhat purer state by Conheim; so far it has not been obtained 

 free from admixture with protein and various metallic salts. It seems 



