218 THE SCIENCE OF BIOLOGY 



of lower animals and in plants. These have long engaged the 

 attention of physiologists, but until recently interest has 

 been centered upon the higher vertebrates. At the present 

 time, zoologists and general physiologists are so engaged 

 with the bio-chemistry and the bio-physics of both the 

 simpler and the more complex organisms that the intelligent 

 reading of many zoological papers demands as much or more 

 knowledge of physics and chemistry as of natural history. 

 It may be noted, as a sign of the times, that candidates for 

 advanced degrees in zoology are now expected to be well- 

 grounded in chemistry and physics, as well as in general 

 zoology. These physical sciences are important for the 

 zoologist, not only because they afford a knowledge of the 

 facts but also because they foster an appreciation of experi- 

 mental methods. 



The ancient affiliation between the biological sciences and 

 medical science continues. The role of insects in disease, the 

 new sciences of Protozoology and Parasitology, the interest 

 of the medical profession in heredity, the interest of the 

 zoologist in the physiological facts brought out by serum- 

 therapeutics, by the study of endocrine secretions, and the 

 like, are examples that illustrate the many points of contact. 

 Zoology arose in close association with medical science. The 

 more scientific medicine becomes the greater will be its de- 

 mands upon zoological science. Extended medical experi- 

 mentation upon human beings is impossible, though it often 

 happens that the physician sees the end results of such 

 experiments, as when a community begins the use of water 

 from a filtration plant after long experience with water from 

 a contaminated source. The experimental work of medicine 

 must be accomplished mainly by use of animals. Since this 

 experimentation is necessary for the advancement of medical 

 knowledge, medical investigation must deal with zoological 

 material. In the past it has utilized the higher vertebrates, 

 such as the cat, dog, rat, and guinea-pig. As the human 

 mechanism becomes subjected to a more searching examina- 



