BY R. GREIG SMITH. 153 



and that when the calf ceases to be carnivorous and becomes 

 herbivorous, the secretion of rennin ceases. This may be so in 

 practice, but Moro^ found rennin in the mucous membrane of the 

 stomachs of children soon after birth and before feeding. A 

 dead-born child has none. The loss of weight of an animal 

 during the first week or ten days after birth can probably be 

 explained by a certain time being necessary to get the digestive 

 system into working order in response to the stimulus given by 

 the presence of food in the alimentary tract. As we shall see, 

 lactase takes some time before it is secreted. Portier obtained 

 lactase from ducks after they had been fed with lactose for 25 

 days, and Bayliss and Starling say that " the pancreas of new- 

 born animals, for instance, is quite free from lactase, which, how- 

 ever, makes its appearance two or three days after birth as a 

 result of the milk diet. . . . For the production of lactase 

 in the pancreas, or its juice, it is therefore necessary that lactose 

 should act on the intestinal mucous membrane for some time. 

 The reaction is a slow one . 



It is evident from these few examples that digestive enzymes 

 are originally and subsequently formed or secreted both by plants 

 and animals in response to the stimulation made by the presence 

 of the nutrient capable of being acted upon. The presence of 

 food nutrients in the alimentary tract brings forth from the cells 

 of the tract or glands connected therewith the appropriate diges- 

 tive enzymes. 



If dead bacteria were fed, or if living bacteria were killed in 

 a part of the canal, it will not be gainsaid that they would share 

 the fate of the food nutrients. Metchnikoif,t in discussing the 

 role of microbes in the intestine, mentions Klein, Schutz and 

 Kohlbrugge as having found a bactericidal action occurring in 

 the intestine; the latter investigators traced the action to the 

 small intestine. He quotes the results of some unpublished 

 experiments of Delezenne, which showed that neither the pan- 



* Cent. f. Bakt. Orig. xxxvii. 485. 

 t Bull, rinst. Past. i. 217. 



