30 R. H. A. PLIMMER. 



sive evidence that adaptation could occur at all, and would bring down 

 Darwin's environment theory to too narrow an issue, when such 

 processes require indefinitely long periods of time. In the experiments 

 on this subject the animals which permanently have lactase are those 

 which are highest in the scale, namely man, monkey, the carnivora and 

 omnivora, &c. The more functions an animal can perform, the higher it 

 must be in the scale of organised beings. It does not seem impossible 

 therefore that adaptation could be experimentally attained by prolonging 

 the stimulus for very much longer periods, i,e. through many generations 

 of animals instead of on one animal. 



It might be thought that the amount of stimulus given to the 

 smaller animals by feeding was insufficient, as the guinea-pigs and 

 rabbits did not care about bread and milk diet. Through the kindness 

 of Drs C. J. Martin and Dean, to whom I should like to express my 

 thanks, an adult pig was kept for me at the Lister Institute and fed for 

 3 months on 4 gallons (= about 20 litres) of milk per day. This 

 experiment was commenced before I had examined the intestine of a pig 

 for lactase, the previous observers, Portier and Mendel, having been 

 unable to detect the presence of this enzyme, whereas Weinland found 

 it and I could not accept his results. In the meanwhile I examined 

 other pigs' intestines for lactase and found it present, so that the above 

 experiment was really of no use for determining whether adaptation of 

 the intestine occurred. The experiment, however, gave me the oppor- 

 tunity of again investigating whether adaptation of the pancreas occurred. 

 It showed 122 per cent, hydrolysis. Nearly the same amount of 

 hydrolysis, 10'6 per cent., was given by the pancreas of an ordinary pig 

 not fed on milk, and hence it may be concluded that adaptation does aot 

 occur even with this great stimulus. The roughly 10 per cent, hydrolysis 

 in each case is due to contamination from the intestine, since the 

 animals had to be killed in the slaughter-house where it is impossible 

 to prevent contamination when dealing with such large masses of 

 material, and where other animals have previously been killed. The 

 hydrolysis would have been much greater if it were really due to the 

 pancreas itself, which weighed about 150 gins. It was thought that the 

 increase in the amount of reducing sugar might be due to reducing 

 sugar from the pancreas itself, but experiments carried out in exactly 

 the same manner with the pancreas alone and with a solution of glucose, 

 instead of lactose, showed no difference in the amount of reducing sugar 

 after the period of incubation. 



It may therefore be concluded that neither the pancreas nor the 



