DIGESTION. 75 



the natural ones and those producing what alone may be termed 

 normal gastric juice, are food and drink. 



Normal gastric juice has been procured by feeding an animal 

 a fictitious meal. In this process the food swallowed does not reach 

 the stomach, but passes out of the oesophagus through a fistula. 

 The eating has the power to excite reflexly the flow of the secretion. 



Gastric juice thus obtained from a dog is a "clear, colorless, 

 limpid fluid, very acid, and peptic in nature. The liquid is prac- 

 tically odorless; if there is any odor at all present it is character- 

 istic of the animal. Its specific gravity differs very little from that 

 of water" (1002.5). The quantity of gastric juice secreted daily is 

 about one-tenth the weight of the body. 



The largest constituent of the gastric juice is water. In man 

 and animals it is remarkable to note the small quantities of solid 

 matters present and then view the immense amount of work done 

 by them in the digestive processes. Of the solids present, about half 

 are inorganic salts; the remaining portion comprises the organic 

 ferment, or enzyme, present in gastric juice pepsin. 



The reaction of gastric juice is undoubtedly acid, caused by the 

 presence of free hydrochloric acid (0.2 per cent.). In the purft 

 secretion, free from food, it has been demonstrated that the only 

 acid is hydrochloric. Acid is necessary, for pepsin, the active fer- 

 ment of gastric juice, can act only in an acid medium. During 

 digestion, lactic, acetic, butyric, and other acids are often present, 

 due to putrefactive changes and the presence of bacteria. Pepsin 

 can act in the presence of these acids as media, but not very well. 



Schmidt's analysis of the composition of gastric juice is as 



follows: Water 994 40 



Solid residue 5.60 



Organic matter: 1000.00 



Pepsin 3.19 



Inorganic matter: 



Chloride of sodium 1.46 



Chloride of potassium 0.55 



Chloride of calcium 0.06 



Free hydrochloric acid 2.00 



Phosphate of calcium "j 



Phosphate of magnesium > 0.12 



Phosphate of iron J 



Secretion of the Gastric Juice. 



Imbedded in the mucous membrane of the walls of the stomach 

 are two sets of secretory apparatus: the cardiac and pyloric glands. 

 Naturally the products of these glands differ somewhat in their char- 

 acters- so that the gastric secretion as a unit is a mixed body, or solu- 



