298 CHEMICAL MECHANISMS OF SECRETION 



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 

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

 of the milk in the intestine. 



Similar variations 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 

 protein, 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 protein but scarcely any carbo- 

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

 digesting protein increases from day to day, while the digestive 

 power for starch progressively diminishes. On reversing the diet 

 again to bread and milk, similar but inverse changes are observed. 

 The moral from this for practical medicine, which experience had 

 already indicated, is that a sudden change from one regime to 

 another may have a disastrous effect upon the digestive process, 

 by subjecting the glands to a strain to which they have not been 

 adapted. Hence changes in dietary should be brought about 

 slowly and progressively wherever possible, and not by a sudden 

 and sweeping change. 



The physiological causes and mechanisms of this interesting 

 adaptation in quantity and quality of the digestive fluids to the 

 nature of the food are as yet obscure to us. 



Pawlow, their chief discoverer, ascribed them to a differentiated 

 peripheral nerve-supply in the mucous membrane of the alimentary 

 canal, whereby the absorption of different digested food- stuffs 

 stimulated different nerve endings, fibres, and cells, and caused 



