THE " SEXUAL SEASON " OF MAMMALS. 49 



are cut off, as it were, by tlie extravasated blood, from the 

 deeper mucosa cells, and they shrivel up and die. Soon the 

 uterine epithelium follows suit and, with the degeneration of 

 its cells, loses its continuity and ruptures, thus allowing the 

 blood hitherto contained to pour into the uterine cavity. 



Stage VII. The formation of the menstrual clot. With 

 the blood which is poured out from the ruptured lacunse is 

 mixed also degenerated epithelium cells, isolated or in strings ; 

 and as the tissue below is laid bare, the extravasated blood in 

 the deeper parts of the mucosa, together with stroma tissue 

 and the superficial portion of uterine glands, also collects in 

 the uterine cavity, and the whole forms therein a more or less 

 dense clot. Some of the blood and degenerate uterine tissue 

 oozes out through the os uteri to the vagina and thence to 

 the exterior while the process is in progress, but there is fre- 

 quently left behind until a later stage a clot, which in some 

 cases entirely fills the uterine cavity. 



D. Periodof Recuperation, — Stage VIII. The recupera- 

 tive stage. While the clot is still within the uterus, a new epi- 

 thelium begins to grow over the, now much reduced, uterine 

 stroma. At the same time new capillary vessels are formed, the 

 extravasated blood which still remains in the tissues is collected 

 therein, and brought back into the circulatory system. 

 During this period the clot is expelled, and subsequently the 

 uterus assumes again the appearance first described, and 

 eventually becomes again at rest. It is at or towards the 

 close of this period that oestrus normally occurs. 



For the human female the histology of pro-oestrum (men- 

 struation) has never been so fully worked out in healthy normal 

 uteri. Many observers have described isolated specimens, 

 and most of them have had recourse to material which has 

 either been obtained some time after death, or from indi- 

 viduals suffering from diseases which may well have produced 

 pathological changes in the uterine tissue. Then, again, the 

 extent of menstruation varies in different peoples and indi- 

 viduals, and in the same individual at different times. The 

 amount of the menstrual flow and the quality of that flow also 



VOL. 44, PAKT [. — NEW SERIES. D 



