THE PITUITARY BODY 



signs of oestrus. Such a precocious oestrus can be produced 

 in mice 15 days old (after five implants) or in rats 22 days old 

 (after eight implants).' Older animals invariably respond 

 more quickly. 



The changes in the ovaries of immature mice or rats re- 

 ceiving implants are the most striking part of the effects. 

 They may be enormously increased in size, weighing ten (rat) 

 to nineteen (mice) times as much as ovaries of normal litter- 

 mate animals. The implanted anterior-pituitary tissue liber- 

 ates hormone(s) which appear initially to cause ovarian hy- 

 peremia, and follicular growth and maturation. Many folli- 

 cles may become fully ripe at the same time, rupture, and lib- 

 erate as many as forty-eight ova (superovulation of Smith 

 and Engle). On the other hand, only folHcular growth with- 

 out ovulation frequently occurs (Zondek and Aschheim). 

 Corpora lutea are then formed either from ruptured or un- 

 ruptured follicles. In the latter case the lutein cells are large- 

 ly derived from the granulosa and grow about the degener- 

 ating ovum, thus forming corpora lutea atretica.^ The in- 

 creased ovarian weight is due both to follicular growth and to 

 the formation of corpora lutea (see Fig. 28). 



The completion of vaginal canalization and the appearance 

 in the vaginal smear of the nucleated and/or cornified cells 

 characteristic of oestrus are due to the liberation of the fol- 

 licular hormone (©estrone, oestradiol?). This hormone hke- 

 wise causes a marked hypertrophy of the uterus, largely due 

 to a distension by fluid, which is also characteristic of oestrus. 

 There is unquestionably a marked increase in the amount of 

 the uterine tissue; for the uterine weight is increased 2.5-6.0 



^ "Sexual maturity" probably does not occur in normal female mice at an age of 

 less than 28 days. In normal female rats the earliest age of sexual maturity is prob- 

 ably 34 days. In some colonies the average ages of sexual maturity were found to 

 be: mice, 35 days; rats, 72 days (Engle and Rosasco; Long and Evans). 



3 Swezy (1933), like others, believed that most of the lutein cells of corpora 

 lutea atretica arise from the theca interna. 



