THE GASTRIC JUICE. [CH. xxxi. 



Action of Gastric Juice. 



The principal action of the gastric juice consists in converting 

 the proteids of the food into the diffusible peptones. In the case 

 of milk this is preceded by the curdling due to rennet (see p. 458). 



There is a still further action that is, the gastric juice is 

 antiseptic ; putrefactive processes do not normally occur in the 

 stomach, and the organisms that produce such processes, many 

 of which are swallowed with the food, are in great measure 

 destroyed, and thus the body is protected from them. The acid 

 is the agent in the juice that possesses this power. 



The formation of peptones is a process of hydration ; peptones 

 may be formed by other hydrating agencies like super-heated 

 steam and heating with dilute mineral acids. There are certain 

 intermediate steps in this process : the intermediate substances 

 are called pro-peptones or proteoses. The word ' proteose ' is the 

 best : it includes the albumoses (from albumin), globuloses (from 

 globulin), vitelloses (from vitellin), &c. Similar substances are 

 also formed from gelatin (gelatinoses) and elastin (elastoses). 



Another intermediate step in gastric digestion is called para- 

 peptone : this is acid albumin or syntonin. The products of 

 digestion may be classified, according to the order in which 

 they are formed, as follows : 



1. Parapeptone or acid albumin. 



( (a) Proto-albumose \ Th f e , P^ albumoses, i.e 



2 . Propeptone \ (6) Hetero-albumose | jjj" whlch are formed 



\(c) Deutero-albumose 



3. Peptone. 



It is doubtful whether all the proteid present passes through 

 the acid-albumin stage. 



The primary albumoses are precipitated by saturation with 

 magnesium sulphate or sodium chloride. Deutero-albumose is 

 not ; it is, however, precipitated by saturation with ammonium 

 sulphate. Proto- and deutero-albumose are soluble in water ; 

 hetero-albumose is not ; it requires salt to hold it in solution. 



Peptones. These are the final products of the action of 

 gastric juice on native proteids. 



They are soluble in water, are not coagulated by heat, and are 

 not precipitated by nitric acid, copper sulphate, ammonium sul- 

 phate, and a number of other precipitauts of proteids. They are 

 precipitated but not coagulated by alcohol. They are also 

 precipitated by tannin, picric acid, potassio-mercuric iodide, 

 phospho-molybdic acid, and phospho-tungstic acid. 



