CHAPTER VI. 



GASTRIC DIGESTION. 



GASTRIC digestion takes place in the stomach and is promoted by 

 the gastric juice, which is secreted by the glands of the stomach 

 mucosa. These glands are of two kinds, fundus glands and pyloric 

 glands which are situated, as their names imply, in the regions 

 of the fundus and pylorus. The principal foods acted upon in 

 gastric digestion are the proteins which are so changed by its pro- 

 cesses as to become better prepared for further digestion in the 

 intestine and for their final absorption. 



From reliable experiments made upon lower animals it is evident 

 that the gastric juice is secreted as the result of stimuli of two 

 forms, i. e., psychical stimuli and chemical stimuli. The psychical 

 form of stimuli may be produced by the sight, thought or taste 

 of food, and the chemical stimuli may be produced by certain 

 substances such as water, the extractives of meat, etc., when com- 

 ing in contact with the stomach rnucosa. The volume of gastric 

 juice secreted during any given period of digestion, varies with the 

 quantity and kind of the food. These conclusions were deduced 

 principally from a series of so-called delusive feeding experiments. 

 A dog was prepared with two cesophageal openings and a gastric 

 fistula. When thus prepared and fed foods of various kinds such 

 as meat and bread, the material instead of passing to the stomach, 

 would invariably find its way out of the animal's body at the upper 

 cesophageal opening. Through the medium of the gastric fistula 

 the course of the secretion of gastric juice could be carefully 

 followed. It was found that when the dog ate meat, for example, 

 there was a large secretion of gastric juice notwithstanding no por- 

 tion of the food eaten had reached the stomach. Further experi- 

 ments made through the medium of a cul-de-sac formed from the 

 stomach wall have given us many valuable conclusions, among 

 others those regarding the influence of the chemical stimuli. The 

 method followed was to feed the animal certain substances and 

 note the secretion of gastric juice in the miniature stomach while 

 the real process of digestion was taking place in the stomach proper. 



Normal gastric juice is a thin, light colored fluid which is acid 



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