CHEMICAL MECHANISMS OF SECRETION 297 



of food. Each, food possesses a modifying effect both upon the 

 quantity and quality of the secretion. Also the presence of one 

 food has a modifying power upon the secretion called forth by 

 another, and on the whole course of digestion. 



Thus in the case of gastric secretion on a meal of flesh, bread, 

 or milk respectively, each separate food corresponds to a definite 

 hourly rate of secretion, and calls forth a characteristic alteration 

 of the properties of the juice. Flesh and bread diet produces 

 a maximum rate during the first hour of digestion, while milk 

 gives the maximum rate during the second or third hour. Tested 

 as to maximum content in ferment during the period of digestion, 

 the greatest activity is found with flesh diet in the beginning ; 

 with bread in the second and third hours ; and with milk in the 

 last (or sixth) hour. Contrasting the digestive power of the juices 

 for protein at corresponding periods of digestion in the case of 

 the three foods, the greatest power is found in the case of the flesh 

 diet, the bread comes second, and, in the earlier stages at least, 

 close to the meat, while that on the milk diet is much feebler in 

 proteolytic power. 



In the case of the pancreatic secretion, a similar adapta- 

 tion of the secretion to the nature of the food is seen, and here 

 the changes become more striking, because there is a ferment for 

 each class of food-stuff, and relative variations can be contrasted. 



The following table of results by Walther, quoted by Pawlow, 

 gives the variation in secretion (quantity and ferments) of pan- 

 creatic juice on milk, bread, and flesh respectively. The quantities 

 of each food given are based on the percentages of nitrogen con- 

 tained in each variety : 



The adaptation of the secretion to the nature of the food 

 requires no comment. Attention may be drawn to the high pro- 

 teoclastic power of the secretion called forth by the milk, and 

 to a contrast of this with the low proteoclastic power produced 



