GENETIC TYPE AND THE ENDOCRINES 



of glandular secretion relieves the deficiency and restores the 

 entire internal chemical environment to normal, and by so 

 doing facilitates the proper growth response. Growth is a 

 universal property of protoplasm or life itself and occurs 

 even where no specific pituitary hormone is known to exist. 

 It scarcely seems logical to imagine the phenomenon of growth 

 as depending specifically upon such a hormone, though of 

 course it may be that in higher animals the kind and degree 

 of growth is regulated, controlled and modified by it. In the 

 developing body there most certainly must exist a very definite 

 mechanism for insuring coordination of growth among the 

 various organs and systems in order to bring* about the 

 harmonious size relations of all its parts and finally to limit 

 increase in total size at a characteristic level. Very probably 

 the function of the pituitary gland is highly significant in 

 this adjustment of proportions and limit in body mass. Much 

 material bearing directly upon these problems is presented 

 in this study. 



The bulldog calf of Crew and the creeper-fowl or "parrot 

 chicken" of Landauer are quite different from the dwarf 

 mouse of Smith and MaeDowell and the well known thyroid 

 cretin. In the former cases, the extremities and the skull 

 undergo a marked modification of development during early 

 embryonic stages and this distorted development is inherited 

 in definite Mendelian manner and cannot be changed to the 

 normal type by any form of glandular administration yet 

 attempted. 



For many years I have been investigating modifications of 

 embryonic growth and development brought about by various 

 chemical disturbances of the embryonic environment. These 

 studies finally led to the problems involved in an analysis 

 of those changes during postnatal growth which establish the 

 individual type and constitution. In studying such problems, 

 it becomes strongly evident that the differences in genetic 

 composition among individuals have so great an influence in 

 determining their response to any modifying cause that an 

 understanding of postnatal development and final expression 



