CHANGES IN NON-PREGNANT UTERUS 103 



marked correlation between the cyclical uterine changes and the 

 developmental cycle in the corpora lutea of the ovaries (see p. 38). 

 During the second week after a heat period the cells of the 

 uterine and also the vaginal mucous membrane begin to show 

 signs of degeneration and the process of desquamation commences. 

 At the completion of two weeks the mucosa undergoes " wholesale 

 destruction," but it is not clear whether this is to be regarded as 

 procRstrous or pseudo-pregnant degeneration, or whether it is a case 

 of the two processes being compressed into one such as may possibly 

 occur in man. 1 



Cyclical changes in the sexual organs of the rat have also 

 been described by Long and Evans, 2 and by Kirkham and Burr. 3 



THE CYCLE IN UNGULATES 



The uterine changes have been worked out in the sheep and in 

 the sow. As described in the former 4 they relate chiefly to the 

 blood-vessels, and are grouped according to four periods as in the 

 case of the monkey, the dog, and the ferret, referred to above. 



(1) 7V/-/W ii f Jie.*t. The histological characters of the uterus 

 during this period are those of an organ in a state of quiescence. 

 Protoplasmic processes can be seen passing from certain of the stroma 

 nuclei, but these, though denser in some places than in others, show 

 littlp evidence of division. Dark brown or black pigment may be 

 present in considerable quantities, especially in the region subjacent 

 to the epithelium, both in the cotyledonary papilla? and (more 

 frequently) between them and round their bases. Such pigment has 

 not been observed in yearling sheep (i.e. in sheep less than a year 

 old) ; neither does it appear to occur, as a rule, during the ano3strum, 

 but only during the dicr-strous interval. 



(2) Period of Growth. The nuclei in the stroma multiply, and 

 the mucosa increases slightly in thickness. The epithelium, however, 

 appears to remain unaffected. The blood-vessels increase botli in 



1 ( 'yrlir.il changes in the guinea-pig, more particularly in the ovary, \\ere 

 previously described by Leo Loeb("The Cyclic Changes in the Ovary <>f the 

 (Juinea-Pig," /<>"/. of .\fr///>., vol. xxii., 1911). See also Ishii ("Obserwtiona 

 on the Sexual Cycle of the ( iuinea-Pig," Biol. />//.. vol. xxxviii., 1!)20). 



- Long and Evans, "The OCstrous Cycle in the Eat, : .\imt. I!" <>,-<{, vol. xviii., 

 I !>:'<>. 



3 Kirkham and Burr. "The Breeding Habits, Maturation of Eggs, and 

 Ovulation of the Albino Hat," .!/;/. ./<>/: <>f A/'f., vol. xv.. ]!>13. For other 

 work on the tt?strous cycle and sexual periodicity, etc., in Rodents, see abstracts 

 of papers by Long and Evans as well us of papers l>y r'reyer. Sutler, and others 

 in PI-HI-. .I/,/--/'. .Ixxuc. .\/><if., !!:><) and I!J1, Aunt. AV, <//,/, vols. xviii. and xxi. 

 Long and Evans have ckvrribed pseudo-pregnancy in the rat as a result of 

 sterile coition and of mechanical stimulation of the cervical (anal. 



4 Marshall, "The CEstrous Cvc'Ie and the Formation of the Corpus Luteum 

 in the Sheep, 1 ' !>/<>/. Trn,,*.. B.. vol. cxcvL, 1W3. 



