X 



EXPERIMENTAL STUDY OF THE INFLUENCE OF 

 ENVIRONMENT ON ANIMALS^ 



I. INTRODUCTORY REMARKS 



What the biologist calls the natural environment of an 

 animal is from a physical point of view a rather rigid combina- 

 tion of definite forces. It is obvious that by a purposeful and 

 systematic variation of these and by the application of other 

 forces in the laboratory, resxilts must be obtainable which do 

 not appear in the natural environment. This is the reasoning 

 underlying the modern development of the study of the effect 

 of environment upon animal life. It was perhaps not the least 

 important of Darwin's services to science that the boldness of 

 his conceptions gave to the experimental biologist courage to 

 enter upon the attempt of controlling at will the life phenomena 

 of animals, and of bringing about effects which cannot be 

 expected ia nature. 



The systematic physico-chemical analysis of the effect of 

 outside forces upon the form and reactions of animals is also 

 our only means of unraveling the mechanism of heredity 

 beyond the results which can be obtained by a mere cytological 

 investigation. The manner ia which a germ cell can force upon 

 the adult certain characters will not be understood until we 

 succeed in varying and controlling hereditary characteristics; 

 and this can only be accomplished on the basis of a systematic 

 study of the effects of chemical and physical forces upon living 

 matter. 



Owing to limitation of space this sketch is necessarily very 

 incomplete, and it must not be inferred that studies which are 



1 Reprinted from Darwin and Modern Science (1909), by courtesy of Professor 

 A. C. Seward, of the University of Cambridge, England. 



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