CHANGES IN THE NON-PREGNANT UTERUS 89 



in the size of the blood-vessels, and an absorption of the blood 

 which remains extravasated in the stroma. As to how the 

 blood is absorbed has not been determined in the human female. 

 This is a question which will be discussed in considering the 

 regeneration stage in monkeys and in the lower Mammals. It 

 is stated that new capillaries are formed after the close of the 

 destruction. 



The average length of the normal menstrual cycle, as already 

 mentioned, is twenty-eight days. Of these about five are 

 occupied by the pre-menstrual swelling, four by menstruation, 

 and probably about seven by the regeneration process, leaving 

 not more than twelve days for the period of quiescence.^ There 

 can be no doubt, however, that the length of the respective 

 stages must vary according to the extent of the destruction 

 and the amount of tissue which it is necessary to replace. 

 According to Westphalen,^ the regenerative process may last 

 for as long as eighteen days, or until the commencement of the 

 succeeding pre-menstrual swelHng.* 



The Cycle in Monkeys 



The histology of the menstrual cycle in Semnopithecus 

 entdlus and Macacus rhesus has been very fully studied by 

 Heape.* Previously to Heape's work. Bland Sutton ' had paid 

 some attention to the histology of the menstrual process in 

 Macacus rhesus, but without entering into great detail. More 

 recently van Herwerden * has given an account of the cychcal 

 changes of the uterus in Cercocebus cynomolgus. 



' Whitridge Williams, loo. cit. 



^ Westphalen, loc. cit. 



' For further references to the subject of menstruation in the human 

 female the following authors may be consulted : Steinhaus, " Menstruation 

 und Ovulation," Leipzig, 1890; Heape, Phil. Trans. 5., vols, clxxxv. and 

 olxxxviii., 1894 and 1897; Gebhard, "Die Menstruation," Veit's Ilandbuoh 

 der Gyndk., vol. iii., 1898. For an account of the various pathological changes 

 which are known to occur in the human uterus, see Macgregor, A Contriiution 

 to tlie Pathology of the Eiulcrmetrium, Edinburgh, 1905. 



' Heape, loc. cit. 



" Bland Sutton, "Menstruation in Monkeys," Brit. Gt/ncec. Jour., vol. ii., 

 1880. 



' Van Herwerden, "Bijdrage tot de Kennis von den Menstrueelen 

 Cyclus," Tijdschrifl d. Ned. Uicrh. Yereert., vol. x., 1906. 



