THE REGULATION OF GASTRIC SECRETION. 199 



rate of secretion and a characteristic alteration in the prop- 

 erties of the juice. With a meat diet the maximum rate 

 of secretion occurs during the first or second hour, during 

 which periods the quantity of juice secreted is approxi- 

 mately the same. With bread the maximum secretion 

 occurs during the first hour, while with milk it occurs dur- 

 ing the second or third hour. The jiiice has the greatest 

 digestive power during the first hour when meat is fed, 

 during the second and third when bread is given,- and during 

 the last hour when milk is the food furnished " the dog. 

 ^ As the gastric juice acts chiefly upon the protein con- J 

 stituent of the food, PAWLOW has made an interesting cal- 

 culation of the comparative work done by the stomach in 

 digesting the three articles of food mentioned above, taking 

 into consideration the nitrogen content of the foods and the 

 quality and quantity of gastric juice poured out upon them. 

 He finds that the number of ferment units (obtained by 

 multiplying the squares of the numbers representing the 

 digestive strengths by the number of c.c. poured out upon 

 the food) required for the digestion of corresponding nitro- 

 gen equivalents in the different kinds of food is as follows: 



Bread 1600 units 

 Meat 430 " 

 Milk 340 ." 



This means that protein in the form of bread requires 

 five times more ac id-pro teinase for its digestion than is 

 poured out upon the same amount of protein in milk, and 

 that the protein of meat requires a fourth more than its 

 equivalent contained in milk. Now it is known that vege- 

 table proteins are much less easily digested than those of 

 meat, and these less than those of milk. The different * 

 kinds of proteins seem, therefore, to call forth the secretion 

 of quantities of ferment which correspond with the differ- 

 v r ences in their digestibility. 



The concentration of the hydrochloric acid in the gastric 

 juice also varies with the different kinds of food. It is 



