160 MANUAL OF PHYSIOLOGY. 



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, 35 

 40 C. 



The activity of the gastric juice diminishes when the 

 temperature either rises above or falls below this stand- 

 ard. 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. 



All these requisites are found in the normal act of digestion. 

 The temperature of the stomach is 38 to 39 C. (= 100 F.). 

 Hydrochloric acid is present in the proportion of about .2 per cent. ; 

 as quickly as the peptones are formed they can be removed by 

 absorption from the stomach, and thus the needful dilution is 

 accomplished ; and, finally, if the mouth has done its duty, the 



