ACTION ON OTHER CONSTITUENTS OF FOODS. 335 



Mayer). The free hydrochloric acid of the gastric juice is itself 

 sufficient to precipitate it ; the acid removes from the alkali-albuminate 

 or casein the alkali which keeps it in solution. Hammarsten separated 

 a special ferment from the gastric juice quite distinct from pepsin the 

 milk-curdling ferment which, quite independently of the acid, pre- 

 cipitates the casein either in neutral or alkaline solutions. It is this 

 ferment or rennet which is used to coagulate casein in the making of 

 cheese. [Rennet is an infusion of the fourth stomach of the calf in 

 brine.] 



One part of the rennet-ferment can precipitate 800,000 parts of casein. When 

 casein coagulates, two new proteids seem to be formed the coagulated proteid 

 which constitutes cheese, and a body resembling peptone dissolved in the whey. 

 The addition of calcium chloride accelerated, while water retarded the coagu- 

 lation (Hammarsten). See Milk. 



Casein is first precipitated in the stomach, then a body like syntonin is formed, 

 and finally peptone. During the process, a substance containing phosphorus 

 and resembling nuclein appears (Lubavin). 



There is a " lactic acid ferment " (Hammarsten) also present, which 

 changes milk-sugar into lactic acid. Part of the milk-sugar is changed 

 in the stomach and intestine into grape-sugar. 



Action on Carbohydrates. Gastric juice does not act as a solvent of 

 starch, inulin, or gums. Cane-sugar is slowly changed into grape-sugar 

 (Bouchardat and Sandras, 1845, Lehmann). According to Uffelmann, 

 the gastric mucus, and according to Leube, the gastric acids are the chief 

 agents in this process. [Matthew Hay has failed to find any organic 

 ferment in the stomach capable of digesting sugar.] During the 

 digestion of true cartilage, there is formed a chondrin-peptone, and a 

 body which gives the sugar reaction with Trommer's test. Perfectly 

 pure elastin yields an elastin-peptone, similar to albumin-peptone, and 

 hemi-elastin similar to hemi-albuminose (Horbaczewski). 



Fats formerly were stated not to be acted on, but the recent re- 

 searches of Cash and Ogata show that a small part of the fats is broken 

 up into glycerine and fatty acids. 



[We still require further observations on the gastric digestion of fats. Richet 

 observed in his case of fistula (p. 329), that fatty matters remained a long time in 

 the stomach, and Ludwig found the same result in the dog. In some dyspeptics, 

 rancid eructations often take place towards the end of gastric digestion. W. 

 Roberts suggests that there may be some slight decomposition of neutral fats and 

 liberation of fatty acids. In this connection, it is important to remember that 

 fatty acids are liberated from neutral fats by bacteroid ferments (zymophytes).] 



III. Action of Gastric Juice on the 

 various Tissues. 



(1.) The gelatin-yielding substance (collagen) of all the connective-tissues (con- 

 nective-tissue, white fibro-cartilage, and the matrix of bone), as well as glutin, 



