172 Hormones and Heredity 



generation of young rabbits (the offspring of those 

 that had received injections) had the effect of induc- 

 ing the formation of anti-bodies in their blood, which 

 in turn had a specific effect on their germ-cells, espe- 

 cially on the "factors" concerned in lens development. 

 This repercussion may go on generation after genera- 

 tion. The experimenters have also brought forward 

 evidence that suggests that there may be an entail- 

 ment of an acquired immunity to typhoid bacilli. 



HORMONES AND HEREDITY 



One of the most far-reaching of modern discoveries 

 in physiology concerns the role of the ductless or 

 endocrine glands, such as the thyroid gland and the 

 supra-renal body, in the body of Vertebrates. They 

 produce stimulating hormones and quieting chalones 

 which are distributed throughout the body and exert 

 specific influences on particular parts. The chemical 

 messengers thus sent forth exert a regulative action 

 on the functions of the body, securing their orches- 

 tration. If the activity of the thyroid gland is per- 

 turbed there may be a serious loss of bodily and 

 mental health, which can be counteracted for the 

 time being by utilizing in diet or injection the thy- 

 roid glands of sheep and calf. A substance called 

 "secretin," discovered in 1902 by Professors Bayliss 

 and Starling, is produced in the presence of acid by 

 the cells lining the beginning of the small intestine ; 

 it is carried away by the blood-stream, and the par- 

 ticular lock for which it is the key is the pancreas or 



