XIV 
EXPERIMENTAL STUDY OF THE INFLUENCE 
OF ENVIRONMENT ON ANIMALS 
By Jacqurs Logs, M.D. 
Professor of Physiology in the University of California. 
I. Intropuctory REMARKS. 
Wuar the biologist calls the natural environment of an animal is 
from a physical point of view a rather rigid combination 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, re- 
sults must be obtainable which do not appear in the natural environ- 
ment. This is the reasoning underlying the modern development 
of the study of the effects 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 in 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 unravelling the mechanism of heredity beyond the scope of the 
Mendelian law. The manner in 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 in- 
complete, and it must not be inferred that studies which are not 
mentioned here were considered to be of minor importance. All the 
writer could hope to do was to bring together a few instances of the 
experimental analysis of the effect of environment, which indicate the 
nature and extent of our control over life-phenomena and which also 
have some relation to the work of Darwin. In the selection of these 
instances preference is given to those problems which are not too 
technical for the general reader. 
