528 SPECIAL PHYSIOLOGY. 



of the mucous membrane (Bernard). Dr. Beaumont found that, on 

 injecting into the human stomach only 2 oz. of water at 50, the 

 temperature of this organ was depressed to less than 70, and require^ 

 more than half an hour to regain its normal standard, viz., about 100. 

 The specific gravity of the gastric juice, in man, is 1002.5 ; in the 

 dog, 1005. The quantity of solids is about .5 per cent. It is a color- 

 less, or pale yellow, transparent, slightly viscid, and strongly acid 

 fluid, having a faint smell. It resists putrefaction, and is rendered 

 turbid on boiling. Its composition, mixed with a little saliva, is as 

 follows (Schmidt) : 



Water, 994.4 



Pepsin, with other organic matter, '3.2 



Salts, 2.2 



Free hydrochloric acid, .2 



1000. 



The gastric juice of the dog contains ten times as much free acid, 

 and five times as much organic matter ; that of the sheep, six times 

 as much acid, and a little more organic matter ; that of the horse, is 

 somewhat more concentrated. 



The small quantity of solid matter in the gastric juice, is remarka- 

 ble, considering its extremely active powers. The pepsin, its charac- 

 teristic constituent, is a neutral, albuminoid substance, slightly solu- 

 ble in water, forming, on evaporation, a grayish viscid mass, and having 

 a strong affinity for acids. It is precipitated by- tannin, acetate of 

 lead, caustic alkalies, alum, and alcohol. The saline matters consist 

 chiefly of alkaline and earthy chlorides and phosphates. A small 

 amount of lactic acid exists in the gastric juice, but whether as a pro- 

 duct of secretion, or of decomposition, is not certain; by Bernard and 

 others, it is even believed to be the special acid of the gastric juice. 

 Acetic, butyric, and other volatile acids are certainly the result of 

 changes in the food. The presence of free hydrochloric acid is un- 

 doubted, inasmuch as chlorine is found in the gastric juice in larger 

 quantity than the bases which could combine with it; and moreover, 

 this acid has been obtained by the method of dialysis, and therefore 

 independently of chemical decomposition (Graham). Its existence af- 

 fords a singular example of the liberation of a mineral acid from its 

 strongly combined base, by an organic process in the living animal 

 economy. The source of this acid is probably chloride of sodium, or 

 common salt ; and the seat of its decomposition, like that of the form- 

 ation of the pepsin, is probably the soft glandular epithelial cells, or 

 peptic cells ; but it has been suggested, that it may be secreted by the 

 columnar epithelial cells of the upper part of the tubuli and gastric 

 mucous membrane generally (Brinton). It is supposed by Briicke, 

 that the pepsin is neutral when contained in the peptic cells, and be- 

 comes acidified only after its escape from these cells ; for the pepsin 

 obtained from the gastric mucous membrane of the animal, after its 

 acidity has been removed by washing, is neutral. It has also been 

 shown by Bernard, that, whereas the introduction of lactate of iron 



