116 PHYSIOLOGY CHAP. 



hydrochloric acid; but C. Schmidt (1852) first proved it, and 

 showed that the gastric juice of the dog and pig contained chlorine 

 in excess of what was required to combine all the inorganic bases 

 obtained by calcination of the solid residues of the gastric juice. 

 This fact shows that a considerable part of the chlorine is 

 combined with hydrogen in the form of free hydrochloric acid. 



Other acids can be detected in the gastric juice, lactic acid in 

 particular, which is also thought by many to be a secretory 

 product of the gastric glands. Everything, however, points to the 

 probability that lactic acid is a decomposition product of carbo- 

 hydrates produced by special bacteria, that are able to live inside 

 the stomach. The same applies to the butyric acid that has 

 occasionally been found in the gastric juice. 



The amount of hydrochloric acid in the gastric juice varies 

 considerably in different animals. It is much more abundant in 

 dogs ( = 0'46-0*5S per cent) than in man ( = 0'1*7 per cent on an 

 average). But the exact determination of the amount of hydro- 

 chloric acid and its variations during digestion presents serious 

 difficulties, because the acid enters into chemical combination 

 with the proteins introduced into the stomach, the pepsin and the 

 digestive products, and also replaces the phosphoric acid of the 

 phosphates contained in the food. Yet at all phases of digestion 

 the contents of the stomach are acid, because a much larger 

 quantity of hydrochloric acid is always present than is required 

 for combination with the proteins and the bases of the alimentary 

 phosphates. According to Kretschy, Eichet, Uffelmann, the 

 amount of free acid increases constantly during digestion in man. 

 Heidenhain, on the contrary, found no marked differences in the 

 dog in this respect. 



The experiments made with the object of determining the seat 

 of formation of the acid of the gastric juice all point to the 

 conclusion that it is secreted by the glands of the mucosa of the 

 fundus. In fact, in the fasting animal these often exhibit an 

 acid reaction, while the mucous coat of the pyloric portion is 

 alkaline. The value of these observations is, however, impaired 

 by the fact that the pyloric portion always contains a denser 

 stratum of alkaline mucus which may neutralise the acidity of the 

 secretion. That the acid is not formed on the surface as Cl. 

 Bernard supposed, but comes from the secretory cells of the 

 glands, was demonstrated by Briicke on the compound glands of 

 the fowl's stomach. These have a central cylindrical duct into 

 which all the tubules of the gland open, and in which a consider- 

 able quantity of secretion collects. He found that under these 

 conditions the secretion collected within the gland has an acid 

 reaction. 



Heidenhain by indirect arguments arrived at the conclusion 

 that the cells which secrete the acid are the external or border 



