488 



THE GASTRIC JUICE 



[CH. XXXI. 



This last is a distinctive property of proteoses. They are slightly 

 diffusible. 



The above table will give us at a glance the chief characters of 

 peptones and proteoses in contrast with those of the native proteids, 

 albumins, and globulins. 



We see that the main action of the gastric juice is upon the 

 proteids of the food, converting them into more soluble and diffusible 

 products. The fats are not chemically altered in the stomach,f their 

 proteid envelopes are, however, dissolved, and the solid fats are melted. 

 Starch is unaffected ; but cane sugar is inverted. The inversion of 

 cane sugar is largely due to the hydrochloric acid of the juice, and is 

 frequently assisted by inverting ferments contained in the vegetable 

 food swallowed. 



The question has been often raised why the stomach does not digest itself during 

 life. The mere fact that the tissues are alkaline and pepsin requires an acid 

 medium in which to act is not an explanation, but only opens up a fresh difficulty 

 as to why the pancreatic juice which is alkaline does not digest the intestinal wall. 

 To say that it is the vital properties of the tissues that enable them to resist 

 digestion only shelves the difficulty and gives no real explanation of the mechanism 

 of defence. Recent studies on the important question of immunity (see p. 439) 



* In the case of deutero-albumose this reaction only occurs in the presence of 

 excess of salt. 



t According to some recent observations, a small amount of fat-splitting does 

 occur in the stomach. 



