SEXUAL CYCLE OF THE GUINEA PIG. 



247 



On the Duration of the Sexual Cycle following Parturition. 

 The time of the second menstruation in the period following 

 parturition is rather variable as shown in the following table: 



Among 20 guinea pigs in the period following the puerperium 

 I found complete menstruation and heat in 15 cases, while in 5 

 animals I found only menstrual secretion without heat. The 

 majority of these animals suckled their young and among those 

 the deviation from normal was somewhat less; in these cases the 

 duration was mostly 151/2 to 18 days. 



Effect of Lactation and Non-Lactation on the Periodicity of the 

 Sexual Cycle after Parturition. 



In cases in which the young were suckled the next period of 

 heat took place approximately at the normal time and the condi- 

 tions continued from then on in a normal manner. It was dif- 

 ferent in cases in which bodily weakness of the mother prevented 

 the suckling of the young. In the latter cases the return of 

 menstruation was delayed so that it occurred as late as 21 to 23 

 days after parturition. In the normal suckling animal the sexual 

 periodicity following labor is therefore similar to that of the 

 normal animal, although certain minor variations depending on 

 the vitality of the animal occur even in such cases. The second 

 or third menstruations occur usually after the regular interval of 

 15 to 16 days even in the weak animal. In the latter, hbweven 

 we> may at these times instead of heat merely find menstrual 

 secretion. 



The Effect of Suckling on the Mother and the Young. 



Marshall 1 expresses the opinion that in the young separated 

 prematurely from the mother growth will continue. My own 

 observations lead me to a different conclusion. I have found 



1 F. H. A. Marshall, "The Physiology of Reproduction." London, 1910. 



