GASTRIC DIGESTION. 151 



appear probable, however, that it possesses this property to an 

 unlimited extent, since it undergoes no change itself, and with 

 fresh supplies of acid a very minute quantity of pepsin can con- 

 vert an indefinite amount of proteid into peptone. 



The rapidity with which proteid is converted varies according 

 to the circumstances under which it is placed as well as the kind 

 of proteid used. If the same proteid be used the following cir- 

 cumstances will be found to influence the rapidity of the process: 



1. The temperature. As already stated, the optimum degree 



of heat for the change is about that of the body, 38- 

 40 C. 



The activity of the gastric juice diminishes when the 

 temperature either rises above or falls below this standard. 

 The minimum at which it is capable of action at all is 

 about 1 C. and the maximum is about 90 C. Boiling 

 permanently destroys the function of pepsin. 



2. The percentage of acid as well as the kind of acid has a 



marked effect. Though the action will go on with other 

 acids, hydrochloric is the most effective, and that of a 

 strength of .2 per cent. 



3. Large quantities of salts in solution or a condensed solu- 



tion of peptone impede the process, a certain degree of 

 dilution being necessary for the process. In strong solu- 

 tions of proteid, the peptones must be removed by dialy- 

 sis in order to allow of the continuance of the action. 

 This occurs in the stomach by means of the blood and 

 absorbent vessels. 



4. The degree of subdivision to which the proteid has been 



subjected materially influences the rapidity of its con- 

 version into peptone. The more finally subdivided the 

 substance the greater will be the relative extent of sur- 

 face exposed to the action of the digestive fluids. When 

 large masses are introduced into the stomach, the gastric 

 fluid cannot reach the central portions, and their diges- 

 tion must await the completion of that of the exterior 

 part. 



5. Motion aids the action of the foregoing factors. 



