THE PITUITARY BODY 



iodine, or by grafts of the thyroid. Anterior pituitary extract 

 was effective because it contained thyrotropic hormone. The 

 mechanism by which iodine facihtates molting in such ani- 

 mals is not clear; the element produced no morphological 

 change in the thyroid gland. 



After hypophysectomy, repeated molting occurs in snakes 

 {Tham?20phis sirtalisy T. radix) (Schaefer) — the reverse of the 

 effect induced in urodele amphibia. Hellbaum (1936) recent- 

 ly described the effects of hypophysectomy as well as those 

 following the injection of anterior pituitary extract into such 

 snakes. The cytological changes in the anterior pituitary of 

 thyroidectomized snakes {T. radix) were investigated by 

 Siler (1936). 



Recent observations in birds. — After the complete removal 

 of the pituitary from Brown Leghorn cocks, the feathers 

 finally resemble those of thyroidectomized cocks — loss of 

 black pigment of feathers of part of the neck, of the breast, 

 and of the legs. Hill and Parkes (1935), who made this ob- 

 servation, were able to restore the pigment to normal by ad- 

 ministering thyroxine to a hypophysectomized cock. 



The biology of the thyrotropic hormone in mammals. — 

 Numerous experimental observations with a great variety of 

 objectives have been made in mammals. Much of the work 

 only adds adornment to knowledge previously available; in 

 addition, however, new facts have been gathered. The clas- 

 sification of extensions of our knowledge as well as additions 

 to it will now be attempted. 



The efects oj thyroidectomy on the anterior pituitary. — Hy- 

 pertrophy of the pars glandularis, which is often more marked 

 in male than in female animals, usually follows thyroidec- 

 tomy. It is generally agreed that an important histological 

 change in the anterior pituitary is a marked reduction in the 

 proportion of oxyphils. Also there is an increase in the per- 

 centage of cells with an afiinity for basic dyes; such' cells, 

 often first undergoing hypertrophy, may become vacuolated 

 or appear to be filled with hyaline material and usually are 



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