GASTRIC DIGESTION 139 



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 esophageal 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 portion of the food eaten 

 had reached the stomach. Further experiments 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 in 

 reaction and has a specific gravity varying between i.ooi and i.oio. 

 It contains only 2-3 per cent of solid matter which is made up prin- 

 cipally of hydrochloric acid, sodium chloride, potassium chloride, earthy 

 phosphates, mucin and the enzymes pepsin, gastric rennin, and gastric 

 lipase; the hydrochloric acid and the enzymes are of the greatest impor- 

 tance. The acidity of the gastric juice is due to free hydrochloric acid. 

 It was formerly believed that this acid was secreted by the parietal cells 

 of the fundus as well as by the chief cells of both the fundus and pyloric 

 glands. It has been claimed, 1 however, that the parietal cell is the 

 seat o] the formation of the hydrochloric acid. This conclusion is based 

 upon the formation of Prussian blue after the subcutaneous injection of 

 potassium ferrocyanide and ammonium ferric citrate (rabbits and 

 guinea-pigs) and the subsequent (3 to 30 hours) microscopical examina- 

 tion of the gastric mucosa. The acid was shown to be present in the 

 lumina of the gland tubules and in the canaliculi of the parietal cells; 

 traces were also apparently present in the cytoplasm. Later Bensley 

 and Harvey 2 showed by means of dyes which act as vital stains and 

 as indicators very sensitive to alkali that the secretion in the parietal 

 cells is slightly alkaline whereas that in the lumen of the gland proper 

 is very nearly neutral. Therefore, the acid is formed entirely above the 

 level of the gland proper, i.e., in the foveolae and on the surface. Ham- 

 met 3 and still more recently Macallum and Collip 4 have confirmed Miss 

 Fitzgerald's claim that the acid is formed in the parietal cells. 



It was believed that hydrochloric acid was generally present in the 

 gastric juice of man to the extent of about 0.2 per cent. When the 



1 Fitzgerald: Proceedings Royal Society (B), 83, 56, 1910. 

 1 Bensley and Harvey: Biological Bulletin, 23, 225, 1912. 

 3 Hammett: Anatomical Record, 9, 21, 1915. 

 4 Reported before Society of Biological Chemists, Boston, Dec. 27, 1915. 



