CHANGES IN THE NON-PREGNANT UTERUS 111 



arrived at, through failure to realise the unity of the two pro- 

 cesses. 



It has been shown further that although the changes which 

 occur in the uterus during the cycle present a striking similarity 

 in the various mammalian types in which they have been 

 studied, yet there is a considerable amount of variation in the 

 severity and duration of the procestrous phenomena. The 

 extent of the congestion, and the destruction which usually 

 succeeds it, are greatest, as a rule, in the highest Mammals, 

 and comparatively slight in the Rodentia and Ungulata. The 

 histology of the cycle in the lowest Mammals has never been 

 worked out, but, as already mentioned in the preceding chapter, 

 vaginal bleeding has been noticed in Marsupials. 



The purpose or meaning of the proo3strum, and the factors 

 which contribute to its occurrence, will be considered as fully 

 as the present knowledge of the subject permits, after the changes 

 which take place in the ovaries have been dealt with, in a future 

 chapter of this work. It may be at once stated, however, that 

 most authorities are now agreed that the menstrual process is in 

 some sense a preparation for the attachment of an ovum to the 

 wall of the uterus, but opinions differ as to the precise nature of 

 the preparation. On the other hand, it is evident that the 

 changes involved in menstruation are not absolutely essential, 

 since there are records of pregnancy occurring in individuals 

 who had never experienced menstruation. Moreover, there is 

 evidence that the procestrous discharge may be not only of no 

 utility to the organism, but may even become injurious, as in 

 the more severe cases of menstruation among women. 



In view of these facts it may be called in question whether 

 the procestrous changes in the uterus should not be regarded 

 merely as the result of a wave of disturbance which ushers in the 

 period of desire, and is of the nature of a consequence rather 

 than a purpose. This is in accord with Metchnikoff's suggestion, 1 

 that the catamenia in women is essentially a " disharmony " of 

 organisation, which has been brought about as the result of 

 modifications acquired recently in the history of the species. 

 If this is so, a similar explanation must be adopted in the case of 



1 Metchnikoff, The Nature of Man, Mitchell's Translation, London 

 1903. 



