The Corpus Luteum of the Guinea Pig 79 



or the left Fallopian tube in eight young guinea pigs, and at 

 various stages after post-partum oestrus they were injected 

 with chorionic gonadotrophs. Six days later silk threads 

 were inserted through the sterile horn and the sites examined 

 histologically six days afterwards. No evidence of a decidual 

 reaction was obtained but in two animals in which ovulation 

 was induced on the 53rd day of pregnancy the infertile horn 

 was enlarged around the site of irritation. It should be realized 

 that the horn sterilized by ligation at its cervical end is a large 

 flaccid structure containing a fluid and bears no resemblance 

 to the uterus in the early luteal stage. The latter condition was 

 more closely obtained in animals that were semi-sterilized by 

 ligation of the Fallopian tube, but in two of the eight animals 

 treated in this way there was no sign of a decidual reaction. 



Effect on parturition 



Two guinea pigs were injected in very late pregnancy to 

 observe the effects of the presence of induced corpora lutea on 

 parturition. One, which was treated on the 54th day, gave 

 birth to a litter at the expected time, fourteen days later. 

 No evidence of post-partum mating was obtained but when 

 killed three days afterwards the ovaries contained eleven very 

 young corpora lutea. The second animal, injected on the 

 62nd day, produced a litter seven days later. She was killed 

 six hours after parturition and the ovaries, which contained 

 six induced corpora lutea, also had numerous mature follicles 

 awaiting ovulation. There is little to suggest, therefore, that 

 the induced corpora lutea affect the time of onset of parturi- 

 tion or the recurrence of post-partum ovulation. 



Discussion 



The corpus luteum is an endocrine organ whose main 

 function in unmated animals is the regulation of the di- 

 oestrous cycle by means of its capacity to inhibit ovulation. Of 

 all the structures in the body, it is probably the one which 

 has the shortest life, for in normal circumstances it remains 



