Physiology of Animals. 57 



zoologist rarely knows enough chemistry, the chemist 

 rarely knows enough zoology, to enable either to contri- 

 bute much to comparative physiology. And as for the 

 chemical physiologist, expert as to man and mammals, 

 he has too many pressing problems of his own with 

 attractive practical outcome too to be readily tempted 

 aside by the digestive caeca of the star-fish or the mid- 

 gut gland of the snail. One zealous worker in the latter 

 part of the Victorian era deserves to be commemorated, 

 C. F. W. Krukenberg. He realized 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. Particularly 

 notable too has been the work of Verworn on the Pro- 

 tozoa, which form the Ultima Thule of the physiologist. 

 Ingenuity of experiment and fertility in suggestion are 

 characteristic of his work, the results of which are 

 summed up in his stimulating Allgemeine Physiologic 

 (2nd ed., 1897). 



Since the time of Johannes Miiller the science of 

 physiology has become highly specialized, chemical 

 and it is necessary to distinguish several Aspects, 

 separate lines of advance which have the common aim 

 of storming the citadel of life. 



Thus there is the study of the chemical aspect of vital 

 phenomena, generally referred to, not very happily, as 

 chemical physiology or physiological chemistry. With 

 the beginning of this we may associate the names of 

 Wohler and Liebig, and the progress of the study should 

 be connected, on the one hand, with the development of 

 organic chemistry, on the other hand, with the deepen- 

 ing of analysis, which forced the physiologist from the 

 investigation of the functions of organs to an inquiry 

 into the metabolism or Stoffwechsel of the living body. 



To appreciate the importance of even the early steps 

 we must remember that before Liebig' s day the majority 

 of chemists held that their laws did not apply in the 

 world of life, and even the great Liebig himself regarded 

 the chemical processes which occur in organisms as dis- 

 tinctly subsidiary to the operations of the Lebenskraft or 

 vital force. 



