146 HEREDITY AND SEX 



nerves and isolating the glands. The results are the 

 same as when they are left intact. 



This brings us to one of the most interesting chapters 

 of modern physiology, the production and influence of 

 Internal Secretions. 



INTERNAL SECRETIONS 



It has become more and more probable that the effects 

 in question are largely brought about by internal se- 

 cretions of the reproductive organs. These secretions 

 are now called '^hormones" or ''exciters.!' They are 

 produced not only by glands that have ducts or outlets, 

 but by many, perhaps by all, organs of the body. Some 

 of these secretions have been shown to have very re- 

 markable effects. A few instances may be mentioned 

 by way of example. 



The pituitary body produces a substance that has an 

 important influence on growth. If the pituitary body 

 becomes destroyed in man, a condition called gigan- 

 tism appears. The bones, especially of the hands and 

 feet and jaws, become enlarged. The disease runs a 

 short course, and leads finally to a fatal issue. 



The thyroid and parathyroid bodies play an im- 

 portant role in the economy of the human body 

 through their internal secretions. Removal leads to 

 death. A diseased condition of the glands is asso- 

 ciated with at least six serious diseases, amongst them 

 cretinism. 



The thymus secretion is in some way connected with 

 the reproductive organs. Vincent suggests that ''the 

 thymus ministers to certain needs of the body before 

 the reproductive organs are fully developed." 



