INTERNAL SECRETION OF CORPUS LUTEUM 183 



is so short that no adequate time is available for experiment and 

 the same applies in a lesser degree to the pseudo-pregnant 

 period. During the prolonged inhibition of oestrus which is 

 found during lactation there is, however, an adequate oppor- 

 tunity for experimental work. Parkes and Bellerby (505), 

 studying the effects of injection of the oestrus-producing 

 hormone into the lactating mouse (see p. 117), showed that a 

 very considerable oestrus-inhibiting action is set up by lactation. 

 By means of two other experiments, inhibition was found to be 

 directly due to the persistent corpora lutea of lactation. In the 

 first, lactating mice were ovariectomized and the amount of 

 oestrin required to produce oestrus determined ; the ovariec- 

 tomized lactating mouse required but very little more oestrin to 

 produce oestrus than the ordinary ovariectomized mouse. In 

 other words, the oestrus-inhibition set up by lactation had 

 disappeared following ovariectomy (505), showing that the 

 inhibition is set up through the ovary and is not merely due 

 to the heavy drain upon the metabolism which must result from 

 lactation. Since the suckling mouse produces between one-fifth 

 and one-quarter of its own weight per day of milk (505), this 

 drain upon the suckling mouse is enormous. The second set of 

 experiments was performed on unilaterally sterilized mice (500). 

 Such mice were allowed to become pregnant and to suckle their 

 litter in the ordinary way. During lactation, the ovary contain- 

 ing the corpora lutea was removed and the sterilized ovary 

 without corpora lutea left. This sterilized ovary (see p. 143 

 and p. 175), is capable of carrying on all ovarian endocrine 

 functions other than those performed by the corpus luteum. In 

 the lactating mouse containing the sterilized ovary only, the 

 oestrus inhibition was negligible. These experiments showed 

 clearly that the oestrus-inhibition set up by lactation is per- 

 formed through the corpora lutea, which are caused to become 

 persistent by the act of lactation. 



(c) SENSITIZATION OF THE UTERUS 



Post-cestroits development of the uterus. The classic work of 

 Fraenkel (208-11) on the rabbit made it known that the presence 

 of the corpus luteum is necessary for the attachment of the 



