THE PITUITARY BODY 



changes in both structures following the injection of oestrin, 

 however, are as readily observed in hypophysectomized as in 

 spayed rats (Smith, 1932). 



Pregnant rats have been hypophysectomized by Pencharz 

 and Long (1933), Selye, Collip, and Thomson (1933), and 

 Bergmann (1934). Parturition can occur in the absence of 

 the pars neuralis even if the latter has been removed weeks 

 before the termination of pregnancy (Smith, 1932). Im- 

 plantation is prevented if hypophysectomy is performed not 

 more than 4 days after coitus. Death and resorption of the 

 fetuses occur in rats hypophysectomized 7-10 days after 

 impregnation, Hypophysectomy between the tenth and 

 twentieth days of pregnancy results either in fetal death and 

 resorption or in a prolongation of the pregnancy from the 

 normal period of 21-22 days to a period of 24-26 days. 

 Dead or living young may then be born. Normal parturi- 

 tion occurs in rats hypophysectomized on the twenty-first 

 day of pregnancy. It is not clear exactly why hypophy- 

 sectomy should lead to a prolongation of the period of ges- 

 tation. The corpora lutea of pregnancy appear normal his- 

 tologically. The uterus, however, is said to be less sensitive 

 to the oxytocic principle of the pars neuralis. 



The mammary glands of hypophysectomized pregnant 

 rats undergo hypertrophy; the secretion of milk sets in im- 

 mediately postpartum only to cease a few hours later. If the 

 uterus of the pregnant rat is emptied, lactation sets in and 

 continues for ^^ hours, but not if hypophysectomy has also 

 been performed (Collip and others, 1933). If the lactating 

 rat is hypophysectomized, the secretion of milk ceases within 

 24 hours (Jeffers, 1935). The pituitary, therefore, must be 

 intact if the secretion of milk is to continue; the growth of the 

 mammary gland, however, can occur in the absence of the 

 pituitary. 



The changes in the anatomy and physiology of the thyroid 



[56] 



