THE DEEPENING OF PHYSIOLOGY. 297 



far back as the second century we find Galen dis- 

 secting and experimenting on pigs and monkeys, and 

 arguing tlience to man, then a forbidden subject to 

 biological analysis. But apart from such premoni- 

 tions there was practically no comparative physiol- 

 ogy until Johannes Muller showed that organisms of 

 high and low degree threw light on one another. 

 Prompted by this great master there have been many 

 students of comparative physiology, though few have 

 given themselves wholly to it. Thus comparative 

 physiology lags far behind comparative anatomy ; and 

 no one has done for the former what Gegenbaur, for 

 instance, has done for the latter. This is partly due 

 to the intrinsic difficulties of dealing with the phys- 

 iology of the lower animals (not to speak of plants) 

 where division of labour is less marked. And an- 

 other reason, as we have pointed out elsewhere,* is 

 that the zoologist rarely knows enough chemistry, 

 or the chemist enough zoology, to enable either to 

 contribute much to comparative physiology. 



^^ One zealous worker in the latter part of the Vic- 

 torian era deserves to be commemorated, C. F. W. 

 Krukenberg. He realised the dignity of the problem 

 to which he set himself, and the results recorded in 

 his Studien and Vortrdge remain a monument to the 

 industry of an unfortunately short life." f But the 

 example he set is being enthusiastically followed by 

 men like Cuenot, Verworn, and Loeb, and the contri- 

 butions of older workers like Kowalewsky and Met- 

 chnikoff help to sustain the Miillerian tradition. 



As an illustration of the value of comparative 



work we may refer to another of the enigmatical 



organs of the human body — the thymus gland. In 



* Science of Life, 1899, p. 57. 

 t Thomson, loc. cit., p. 57. 



