CHEMICAL MECHANISMS OF SECRETION 193 



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 

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

 to a contrast of this with the low proteoclastic power produced 

 by milk in the case of the gastric secretion. In the case of flesh 

 there is the reverse effect. It looks from the figures as if the 

 proteid of the flesh were digested chiefly in the stomach and that 

 of the milk in the intestine. 



Similar variation in the curve of rate of secretion and time 

 are found in the case of the pancreas as in the stomach, the curve 

 being characteristic for each food. The form of this curve is 

 altered by the simultaneous presence of different food-stuffs ; thus 

 the curve of gastric secretion for lean meat consisting chiefly of 

 proteid, becomes profoundly modified if a small amount of fat 

 or oil be also given : the rate of secretion and amount of pepsin 

 being reduced, and the maximum point of secretion being pushed 

 back to a later point in the period of digestion. Similarly the 

 curve of secretion for flesh is modified by the addition of starch 

 to the flesh meal, so as to come to resemble fairly closely that of 

 a bread meal. 



4. When an animal is kept for a long period (some weeks) upon 

 a definite and constant diet, the ferment content of the pancreatic 

 juice becomes adapted to the character of the food. If, for example, 

 an animal which has been fed for some weeks entirely upon bread 

 and milk is brought on to an exclusively meat diet, which in contrast 

 with the other diet contains more proteid but scarcely any carbo- 

 hydrate, it is found that the power of the pancreatic juice for 

 digesting proteid increases from day to day, while the digestive 

 power for starch progressively diminishes. On reversing the diet 



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