DIOESTROUS CYCLE IN THE GUINEA-PIG 235 



tion. In the literature only Schulz ('29), according to Bischoff 

 ('52), denies this fact. 



No typical rhythm has been established so far for the subse- 

 quent o\njlations in the guinea-pig. All observers who have 

 examined a number of o\ailations found great differences in the 

 supposed periods of time intervening between two ovulations as 

 we have reviewed in detail above. The numbers give no evi- 

 dence of a regular periodicity in the ovulation process but on the 

 contrary would lead one to beheve that the greatest irregularity 

 in time intervals was the rule. 



On the other hand, really no observations exist to show any- 

 thing like the occurrence of periodic changes in the uterus and 

 vagina accompanying the retiurn of the heat periods. Such a 

 thing as a regular oestrous or preoostrous flow is completely 

 undiscovered in these animals. 



Konigstein ('07), has examined sections of the uterus and 

 vagina of a guinea-pig, and Blair-Bell ('08), has drawn com- 

 parisons giving many interesting observations, but they failed 

 entirel}', or made no attempt, to observe the regular reappear- 

 ance of a definite order of changes in either the uterus or vagina 

 of this animal. 



3. OBSERVATIONS ON THE LIVING ANIMALS 



During the past six years we have been using guinea-pigs in an 

 extensive breeding experiment and it has become more and more 

 evident as om' work goes on that the existing notions of the ovula- 

 tion periods in these animals are of no practical value, or are 

 practically incorrect. In a number of the experiments it be- 

 came important to know accurately when the females ' came into 

 heat' and when ovulation took place. We had concluded, from 

 numerous observations as well as theoretically, that the female 

 guinea-pig very probably had a definitely regular and periodic 

 sexual cycle if it could be worked out exactly. On account of 

 the need of this exact information, we have studied the oestrous 

 cycle in these animals during the past eighteen months. 



Most other attempts at a solution of this problem have cen- 

 tered in a study of the ovary which necessitated either its removal 



