152 ORIGIN OF NATURAL IMMUNITY, 



Before doing so, however, let me bring forward the subject of the 

 production of enzymes. 



Oppenheimer,* after discussing the production of enzymes, 

 says : — " The mould-fungi produce no ferments so long as they 

 are grown upon media from which they can directly supply 

 their wants; but they immediately develop proteoh^tic enzymes 

 when they are cultivated upon a culture medium containing 

 albumin, diastase when they are supplied with starch, and so on." 

 In the higher plants it is known that there are no enzymes in the 

 resting seed, and that under suitable conditions of moisture and 

 temperature the presence of food, capable of being digested, 

 determines the formation of the digestive ferments. In the 

 animal body it has been found that the digestive enzymes of the 

 stomach are secreted in response to the presence and even to the 

 sight of food; and furthermore, the nature of the food appears 

 to cause the secretion of the appropriate digestive enzyme. 

 Bayliss and Starling,! in discussing the alteration of the 

 pancreatic enzymes according to the nature of the food, quote 

 the experiments of Pawlow and his pupils, which show^ed that a 

 starchy food caused a rise in the amylolytic power, and a meat 

 food a rise in the proteolytic power, and fats in the fat-splitting 

 power. While doubting the accuracy of the conclusions concern- 

 ing the proteolytic secretions, they considered that " there seems 

 no reason to doubt the results obtained by these workers as 

 regards the starch-digesting power of the juice." 



This, however, applies to a case or cases in which the digestive 

 apparatus has been acting for some time, and not to the original 

 production of the ferments. I understand that renninf is 

 obtained from the stomachs of calves which have digested milk, 



* Ferments and their Actions, p. 78. 

 t Proc. Roy. Soc. 1904, Ixxiii. [494] 318. 

 * Rennin is not a digestive enzyme in the ordinary sense, although it 

 undoubtedly is one, for does it not split up casein into paracasein and a 

 soluble albuminoid or albumose '? This partial digestion appears to be the 

 function of rennin in the animal stomach. The faeces of children fed solely 

 with cow's milk appear to consist chiefly of paracasein. 



