GENETIC TYPE AND THE ENDOCRINES 19 



ing cause for so common a phenomenon as the changes during 

 mammalian puberty. One can only say in general that these 

 changes result from a biologically harmonious state which 

 develops with time. (A more completely indefinite state- 

 ment would be difficult to compose!) The progressive de- 

 velopment and change in the constitutional nature of the 

 individual is the only determining or causative element in 

 the response of which we are certain. 



In many cases the removal and transplantation of endo- 

 crine glands bring about typical changes in structure and 

 function, but these changes in themselves do not necessarily 

 show the extent to which the particular gland under con- 

 sideration is ordinarily responsible for such processes. The 

 responses are usually brought about by a long series of 

 functional adjustments which develops as a result of the initial 

 operation. Castration, for example, changes the bull into 

 the ox, which is taller, of different form and proportions, 

 and more easily fattened. The accumulation of fat may be 

 caused by changes in the thyroid, pituitary and other glands, 

 as well as the central and sympathetic nervous systems, and 

 is certainly not alone a result of the removal of the gonads. 

 As a matter of fact, similar or probably the same changes 

 may operate to produce fattening of the bull under certain 

 conditions even in the presence of the gonads. Many other 

 questions might be asked and examples enumerated which 

 would strongly indicate that a study of the inheritance and 

 development of peculiar body types in association with modi- 

 fied endocrine quality is a very necessary step towards the 

 full and complete understanding of endocrine reactions in 

 the animal constitution, as well as their role in health and 

 disease. 



Modified types among other domestic animals. Although 

 man and the dog probably show the widest and most highly 

 modified deviations from stem type in size and form, they 

 are by no means the only examples of such phenomena among 

 the domesticated animals. 



