104 THE PHYSIOLOGY OF REPRODUCTION 



size and number, producing uterine congestion. These changes occur 

 both in the cotyledonary papillae and in the intervening tissue 

 around the bases of the papilla?. 



(3) Period of Destruction. The congestion is followed in most 

 cases by the breaking down of some of the vessels. Very frequently 

 the first extravasation takes place from vessels situated immediately 

 below certain parts of the stroma where the nuclei are most thickly 

 distributed: Leucocytes are extravasated along with the red cor- 

 puscles, but there is no evidence of the existence of wandering cells 

 apart from those which are derived apparently from the broken-down 

 vessels. The blood tends to collect below the epithelium. Bleeding 

 into the uterine" cavity may occur, but is not invariable. A few 

 epithelial cells are sometimes torn off (presumably in places where 

 blood is poured out into the cavity), but destruction even to this 

 extent does not necessarily take place. Denudation of the stroma 

 has never been observed. It would seem that the severity of the 

 prooestrous process tends to diminish with each successive dioestrous 

 cycle in the breeding season, and that sometimes in a late prooestrum 

 the period of destruction is never reached, the congested vessels 

 subsiding without undergoing rupture. Bleeding, when it does 

 occur, appears to be more frequent in the cotyledonary papilla? 

 than between them, and is commoner in the large papilla? than in 

 the smaller ones. 



Kazzander } appears to have been the first to detect extravasated 

 blood in the sheep's mucosa. Subsequently Bonnet 2 has noted 

 uterine bleeding in various Ruminants, as well as in the mare and 

 sow, and Kolster 3 has made similar observations (cf. also Emrys- 

 Roberts, see p. 43). Ewart also has described prooestrous extravasa- 

 tion and the presence of heematoidin crystals in the uterus of the 

 mare. Glandular activity during heat was also noted. 4 



(4) Period of Recuperation. The sheep's procestrum may be said 

 to end with the period of destruction, the entire process probably 

 lasting for not longer than one or two days, its exact duration 

 depending upon its severity. (Estrus itself, which occurs during the 

 beginning of the period of recuperation, sometimes occupies only a 

 few hours. 



In those places where bleeding into the cavity took place in the 

 preceding period the epithelium is renewed, apparently from the 



1 Kazzander, " Uber die Pigmentation der Uterinschleimhaut des Schaf es," 

 Arch. f. Mikr. Anat., vol. xxxvi., 1890. 



2 Bonnet, article in Ellenberger's Vergleichende Physiologie der Haussauge- 

 thiere, vol. ii., Berlin, 1892. Cf. also Ellenberger's article in same volume. 



3 Kolster, " Weitere Beitrage zur Kenntniss der Embryotrophe bei Indeci- 

 dunten," Anat. Hefte, vol. xx., 1902. 



4 Ewart, " Studies on the Development of the Horse," Trans. Hoy. 8oc. Edin., 

 vol. li., 1915. 



