92 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



casein is converted into peptones in the usual manner. The 

 value of the curdling process is not apparent. 



Action of Gastric Juice on Foods. (A) On Proteids.A 

 familiar test for the proper performance of gastric digestion is 

 the observation of the effect of the juice in a given case upon 

 the white of an egg (proteid). In normal gastric juice, or in a 

 properly prepared artificial solution, the egg is seen to swell up 

 and dissolve. This soluble proteid is now called peptone, and 

 it differs from the proteid of the egg in certain important re- 

 spects, to be noted later. But, although peptone is the final 

 product of pepsin-hydrochloric action, there are certain sub- 

 stances produced intermediate between the initial proteid and the 

 final peptone, just as in case of the formation of maltose by 

 ptyalin. Some of these substances have been called acid-albu- 

 min, parapeptone, propeptone, etc. But whatever they may be, 

 the nomenclature of Kuhne is being largely followed at present. 

 He supposes that the first product is an acid albumin which he 

 calls syntonin; that syntonin under the influence of pepsin 

 undergoes hydrolysis, taking up water and splitting into primary 

 proteoses ; that each of these primary proteoses takes up water 

 and splits into secondary proteoses ; that these last undergo a 

 similar change with the production of peptones ; so that the suc- 

 cessive substances are proteid, syntonin (acid-albumin), primary 

 proteoses, secondary proteoses, peptones. 



Peptones can be shown to be different from syntonin and 

 the proteoses by chemical reaction. The chief object of proteo- 

 lytic digestion is to get the proteids into a diffusible condition. 

 Peptones differ from proteids in at least three important respects: 

 (i) They can pass through animal membranes, that is, can be 

 absorbed; (2) they are no longer coagulable by heat or many acids; 

 (3) they are capable^ of assimilation by the cells after they have 

 been absorbed. 



(B) On Carbohydrates. There is no enzyme furnished by 

 the stomach to affect any of the carbohydrates. It is true that 



