EXPERIMENTAL ZOOLOGY 199 



of periodic recurrence in biological thought and has returned 

 with renewed vigor within the past decade, though to most 

 working zoologists it seems a dangerous assumption. It may 

 be that this kind of force exists and that finally all will admit 

 it, but most of us prefer for the present to sit in front of the 

 wall which bars our advance, seeking a way through by 

 some knowable means, rather than leave the solid ground of 

 tangible fact and find the way over on the wings of a vitalistic 

 force, mysterious and beyond our powers to analyze. 



With medical studies, the relation of experimental 

 zoology is as intimate today as has been observational work 

 in the past, a striking illustration of this being found in the 

 coming science of protozoology, which has developed upon 

 the foundation laid by the zoologists in their studies of these 

 unicellular organisms and, now that an increasing number of 

 protozoa are known to be the causes of disease, is being pressed 

 alike by the workers in zoology and experimental medicine. 

 Other examples of results which may at any time become 

 points of departure for discoveries of the utmost significance 

 in medicine, are the studies upon development, regeneration, 

 growth, heredity and the like and from the medical side the 

 studies upon immunity, the heredity of disease and the can- 

 cer problem. 



With the social sciences, our relation is still for the 

 most part indirect and the value of experimental or any other 

 zoological work consists largely in the point of view which it 

 gives the student of these lines. The results of biological 

 and medical work in sanitation, disease and inheritance are 

 used by our colleagues along with the rest of humanity, and 

 of course they are ever impatient for the finished product. 

 The conception of the human body as a latter product in the 

 evolution of organic matter has been discouragingly slow in 

 coming to the average human understanding and we have great 

 need today for a wider appreciation of the zoological basis of 

 many human activities. Now that zoology is stepping within 



