THE DIGESTIVE JUICES 75 



and active is the juice secreted, provided the animal is hungry : the 

 psychical element is of great importance. 



THE ACTION OF GASTRIC JUICE 



The principal actions of the gastric juice have been already prac- 

 tically studied : the action of pepsin in converting the proteins of the 

 food into the diffusible peptones is its chief action. The curdling of 

 milk by rennet will be found described in Lesson VI. 



There is still further action that is, the gastric juice is anti- 

 septic ; 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 hydrolysis ; peptones 

 may be formed by other hydrating agencies like superheated steam 

 and heating with dilute mineral acids. There are certain inter- 

 mediate steps in this process ; the intermediate substances are called 

 propeptones or proteoses. The word ' proteose ' is the best to employ : 

 it includes the albumoses (from albumin), globuloses (from globulin), 

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

 from gelatin (gelatoses) and elastin (elastoses). 



Another intermediate step in gastric digestion is .acid-albumin or 

 syntonin. In classifying the products of digestion it will be con- 

 venient to take albumin as our example, but we must remember that 

 globulin, myosin, and all the other proteins form corresponding 

 products. The products of digestion may be classified according to 

 the order in which they are formed as follows : 



1. Acid-albumin. 



((a) Proto-albumose f Th f prima !J a u lbum ses ' 



2. Proteoses \ (b) Hetero-albumose those which are formed 



\ first. 

 \(c) Deutero-albumose 



3. Peptone. 



1. Acid albumin. The properties of the infra-proteins which are 

 the first degradation products in the cleavage of the proteins which 

 occurs during digestion have been described in Lesson V. (see pp. 29 

 and 48). We shall find later that, in pancreatic digestion, alkali- 

 albumin is formed instead of acid-albumin. The theory has been 

 put forward that a protein is capable of playing the part of a base in 



