292 



The Journal of Heredity 



1005^ 



CONTROL M A 

 Brain 





FEMALES 

 Brain Cord 



GROWTH OF BRAIN CONTROLLED BY THYROID GLAND 



Figure 1. In this chart the brain and spinal cord are considered as 

 separate organs of the nervous system. The operated white rats had their 

 thyroid glands and the parathroids removed, and the effect of thyroid removal 

 was determined by a comparison with litter controls fifty days later. The 

 spinal cord, which controls reflex nervous activities of the organism, repre- 

 sents an older and relatively less differentiated part of the nervous system 

 than the brain, in which are centered the higher mental functions. Cretins 

 show a nearly normal development of the "cordal" nervous reactions, but an 

 almost total absence of cerebral functions. These experiments indicate why 

 this should be so. 



cerned in the maintenance of an ade- 

 quate level of this ba.sal metabolism. 

 In addition to, or along with this 

 common type of metabolism, there is 

 evident in each individual organ a 

 specific type which is characteristic 

 for the organ in question in the nature 

 of its assimilative and productive 

 phases. The adrenals produce ad- 

 renin. the ])ancreas secretes trypsin, 



the liver assimilates glucose and stores 

 it as glycogen, and so on. It is prob- 

 able, though not yet demonstrated, 

 that thyroid gland activity has an in- 

 fluence upon the specific as well as 

 the general metabolism o*f the individ- 

 ual organs. It is, however, evident 

 that the thyroid gland, through its 

 relations to the metabolic processes 

 of the body as a whole and of its parts, 



