440 BIOLOGY AND ITS MAKERS 



the biologist is to investigate the architecture of hving beings; 

 then there arise questions as to the processes that occur within 

 the organism, and the study of processes involves the employ- 

 ment of experiments. In the pursuit of physiology exper- 

 iments have been in use since the time of Harvey, but even 

 in that science, where they are indispensable, experiments 

 did not become comparative until the nineteenth century. 

 It now appears that various forms of experiment give also 

 a better insight into the structure of organisms, and the prac- 

 tice of applying experiments to structural studies has given 

 rise to the new^ department of experimental morphology. 



For the purpose of indicating some of the directions in 

 which biology has been furthered by the experimental method 

 of investigation, we designate the fields of heredity and evo- 

 lution, changes in the environment of organisms, studies on 

 fertilization and on animal behavior. 



The recognition that both heredity and the process of 

 evolution can be subjected to experimental tests was a revela- 

 tion. Darwin and the early evolutionists thought the evolu- 

 tionary changes too slow to be appreciated, but now we 

 know that many of the changes can be investigated by 

 experiment. Numerous experiments on heredity in poultry 

 (Davenport), in rats, in rabbits, and in guinea-pigs (Castle) 

 have been carried out — cxperimients that test the laws of 

 ancestral inheritance and throw great light upon the ques- 

 tions introduced by the investigations of Mendel and De 

 \>ies. The investigations of De Vries on the evolution of 

 plant-life occupy a notable position among the experimental 

 studies. 



A large number of experiments on the effects produced 

 by changes in the external conditions of life have been made. 

 To this class of investigations belong studies on the regulation 

 of form and function in organisms (Loeb, Child), the effects 

 produced by altering mechanical conditions of growth, by 



