LACTASE IN INTESTINE. 29 



It has been shown above that neither the frog nor the fowl have 

 lactase in their intestines, and we may conclude that animals lower 

 than mammals do not possess this ferment. Of the mammals, the 

 carnivora and omnivora have lactase present during the whole of their 

 lives, but the herbivora only when they are young, with the exception 

 of the rabbit ; my result in this instance differs from that of Weinland 

 but confirms Portier's. With regard to the pig, neither Portier 

 nor Mendel could find lactase in its intestine, whereas it was found by 

 Weinland whose results are confirmed by my own. Further, I have 

 been able to confirm Bierry and Gmo-Salazar's observation that the 

 ferment does not pass through a Berkefeld filter and is therefore localised 

 in the cells of the mucous membrane of the intestine ; hence the necessity 

 of using extracts such as I have employed. In the cases of the dog, 

 sheep, monkey, calf, pig, only a portion of the mucous membrane of the 

 intestine was used, as the quantity in these animals was too great for 

 convenient manipulation, in all other cases the whole was employed. 



As one \vas able to employ the whole of the intestines of the smaller 

 animals, namely the rat, guinea-pig, and rabbit, a real control was 

 possible for determining whether adaptation had occurred. With the 

 guinea-pig, where the lactase disappears entirely in about 5 weeks after 

 birth, the result that adaptation does not occur is very obvious, the 

 amount of hydrolysis which actually took place, from 0'2 1'5 per cent., 

 being without doubt due to experimental error. In the rabbit and the rat 

 a certain quantity of lactase is always present, but this quantity from 

 the amount of hydrolysis did not increase when they were fed on milk 

 and lactose, and we have thus further evidence that adaptation does 

 not occur. As before mentioned, this evidence could only be obtained 

 by employing the whole of the intestine of the animal in every case, so 

 that a comparison was possible. If adaptation occurred, the percentage 

 of hydrolysis should increase instead of remaining the same as when the 

 animal is not fed with milk, and it never increased to the amount given 

 by the young animal which might at any rate be expected. Thus, 

 a young rat showed 18'5 per cent, hydrolysis and adult rats, fed for 

 various periods, showed 7'2 8'3 per cent, hydrolysis, the same as that 

 given by adult rats which had not been fed on milk. 



The results with the fowl are confirmatory of those with the guinea- 

 pig, rat and rabbit, but the fowl, never having had lactase in its intestine 

 would not be so likely to show any adaptation as would mammals. If, 

 however, adaptation occurred it would be less extraordinary in mammals 

 than in the fowl, and adaptation in the fowl would be the most conclu- 



