SS PROTOPLASMIC ACTION AND NERVOUS ACTION 



and the larval stages in certain animals. That is, certain 

 proteins with a basic or fundamental relation to the 

 organization of the species may be chemically identical 

 in adult and germ; and they may even be distributed 

 spatially in a similar way in both; e.g., with reference 

 to the main axes. In this sense a chemical continuity 

 between germ and adult may exist, corresponding to the 

 morphological continuity. At present, however, we 

 are completely ignorant regarding the details of this 

 correspondence and can only await the results of further 

 investigation. 



EXPERIMENTAL MODIFICATIONS OF GROWTH 

 AND HEREDITY 



If the metabolic production of proteins of specific 

 configuration constitutes the essential chemical basis of 

 growth and development, it must also form the basis of 

 heredity, since by ''heredity" is meant not a separate 

 phenomenon but simply the similarity of the constructive 

 or developmental process in the successive generations of 

 a particular organic species. We may therefore regard the 

 factors of growth as identical with the factors of heredity, 

 and apply the same type of physiological analysis in 

 both cases. 



We find experimentally that while under normal 

 conditions development follows a highly definite and 

 constant course in each species, it can be altered in a 

 definite manner by various procedures; and a large 

 part of experimental embryology is concerned with 

 modifying the growth processes in the germ or embryo 

 and thus controlHng the rate and character of develop- 

 ment. In this manner it has been shown that constancy 



