B. A. HOUSSAY 



cose without the intervention of insulin, but in the great majority of 

 the vertebrates insuhn is a new regulating mechanism of such impor- 

 tance that, when missing, diabetes results, a disease which is fatal sooner 

 or later depending upon the species. Sexuality exists in many inverte- 

 brates without intervention of hormones, but in the vertebrates sexual 

 characters do not reach their full development without the action of 

 ovarian or testicular hormones, the production of which is governed by 

 the pituitary gonadotropins. The functional unity of the organism is 

 assured by nervous and humoral (chemical) mechanisms of correlation, 

 which interrelate the different parts or tissues and regulate their recipro- 

 cal activities. Sherrington has pointed out the unifying integrative 

 action of the nervous system; a similar role is played by the humoral 

 factors, among which are the hormones. Both types of mechanism 

 maintain the stability of the milieu interieur (CI. Bernard) and of the 

 organism as a whole (Cannon's homeostasis) in spite of varying condi- 

 tions in the external environment and in the organism's activity. 

 Modern studies have thus confirmed, extended, and given a more pre- 

 cise meaning to the old and vague notions about the correlations be- 

 tween the organs ("consensus partium" or "sympathies"). 



The roles played by the hormones can be classified somewhat 

 conventionally as follows: 



(7) Metabolism. — Some of the hormones regulate the balance 

 of metabolic processes. Their action may be general (stimulation of 

 oxidation processes by thyroxine) or rather specialized (parathyroids 

 and calcium, insulin and carbohydrate). One and the same hormone 

 may modify several metabolic processes, e. g., adrenal steroids act both 

 upon the metabolism of water and salt, and upon the metabolism of 

 carbohydrates. 



(2) Morphogenesis. — The morphogenetic actions are the con- 

 sequence of the selective role of the hormones in assimilation and 

 growth phenomena. Some endocrine glands such as the pituitary, 

 thyroid, parathyroid, and sexual glands play an important role in 

 growth during a certain stage of development, principally because of 

 their action upon the synthesis of proteins and on the development of 

 bone. In other cases the growth-promoting action is exerted on special 

 organs, as in the case of estrogens which promote the growth of the 

 uterus and mammary gland. 



As the result of growth and differentiation, the proper morpho- 



192 



