400 THE MAINTENANCE OF THE INDIVIDUAL 



anterior part of the gland arises as a dorsal evagination (Rathke^s 

 pocket) from the buccal ectoderm, while the posterior part develops 

 as a downward outgrowth {infundihulum) from the portion of the 

 brain (diencephalon) lying directly over the mouth. The anterior 

 outgrowth in man finally produces the anterior lobe, a small inter- 

 mediate lobe, and a thin layer extending to the brain as the pars 

 tuberalis, while the posterior portion forms the so-called posterior 

 lobe, or pars nervosa. 



The Anterior Lobe 



There appears to be fairly good evidence of the existence of at 

 least five and possibly eight hormones produced by this portion of the 

 pituitary gland. It is probable, since the histology of the gland 

 indicates remarkably little diversity of tissue, that the substances 

 produced are very closely related chemically. 



A. Growth Stimulation. If overactivity of tliis portion of the 

 gland occurs when young, giants will result. On the other hand a 

 similar overactivity arising when adult, results in excessive growth 

 of the bones of hands, feet, and face — a condition known as acro- 

 megaly. The intraperitoneal injection of fresh anterior pituitary 

 extracts resulted in the production of giant rats. Additional evidence 

 has been secured through the autopsies of various giants, who showed 

 a greatly enlarged pituitary. 



B. Gonad Stimulation. During comparatively recent years it 

 has been shown that anterior pituitary implants will produce sexual 

 precocity in sexually immature mammals. This operation has been 

 performed on all of the more common laboratory mammals, includ- 

 ing cats, dogs, and monkeys, and thus far holds for all vertebrates 

 studied. In the female such implants stimulate the development of 

 both follicles and corpora lutea, which are associated with the growth 

 of the female secondary sexual characters. Implants in the male 

 stimulate the development of the semeniferous tubules and inter- 

 stitial tissue correlated with the growth of male secondary characters. 

 These effects, as determined by hormone isolation, are due to two 

 hormones secreted by the anterior pituitary, — one which stimulates 

 the growth of follicles in the ovaries and tubular growth in the case 

 of the male, and the second which produces the formation of the corpus 

 luteum and the secretions of the interstitial cells of the testis. 



C. Lactation Hormone. Knowledge of the existence of this 

 hormone is comparatively recent. Various workers reported that 



