DIOESTROUS CYCLE IN THE GUINEA-PIG 231 



Regarding the occurrence of further heat periods Rein failed 

 to obser\e any regular periodicity. ''Im Eintreten der Brunst 

 habe Ich kcine Periodicitat bei den Versuchstieren bemerkt." 



The foregoing studies are chiefly of historic interest yet they 

 show that these earlier workers recognized the occurrence of 

 ovulation shortl}^ after parturition and were uncertain or con- 

 fused regarding the time or periodicity of subsequent ovula- 

 tions. Little of definite value has ever appeared in the litera- 

 ture to further clear up the last point. We may now briefly 

 consider the more recent contributions which bear on the sub- 

 jects of ovulation and oestrous in the guinea-pig. 



Rubaschkin ('05), gives a detailed description of the sexual 

 conditions in the guinea-pig. He also recognized, as did the 

 earlier observers, that a condition of heat followed shortly after 

 parturition. In almost all females killed a few hours (up to 

 fifty hours) after the birth of a litter an ovulation had occurred. 

 He never observed o^^ulation as early as five hours after parturi- 

 tion though he found fertilized eggs in the oviducts as early as 

 fifteen and seventeen hours after. Copulation occurs directly 

 after ha\'ing given birth to young but for later heat periods 

 Rubaschkin was unable to demonstrate any regular periodicity. 

 ''Es ist mir nicht gelungen, eine bestimmte Frist fiir das 

 Auftreten der Brunst festzustellen." 



He did observe, however, that in some animals ten to twelve 

 days after having given birth to young the entrance of the 

 vagina showed some signs of heat activity. "Oeffnung der 

 Vagina und Rothung der Vaginaloffnung." He claimed that 

 heat ceased to recur after the month of October, at least when 

 the animals were kept in a cold place. The duration of preg- 

 nancy was reported by Rubaschkin in three cases to be ten 

 weeks. 



Rubaschkin thus failed to recognize the regular oestrous 

 cycles in these animals and also states the gestation period some- 

 what too long. 



Konigstein in 1907 recorded the results of observations made 

 on eighteen rats, one guinea-pig and five rabbits. He states 

 that in the rodents heat occurs immediately after giving birth 



