JuLT 13, 1917] 



SCIENCE 



43 



charge is present. The duration of these sev- 

 eral stages is subject in the different animals 

 to individual variations. The first stage, how- 

 ever, is generally longest and lasts from six to 

 twelve hours or even more, and during this 

 time there is a gradually increasing quantity 

 of the mucous secretion which at its height is 

 very abundant and fills the entire lumen of the 

 vagina. The second stage is shorter, lasting 

 from two to four hours, and passes gradually 

 over into the third stage which lasts from four 

 to six hours. The fourth stage is the shortest, 

 only about one to two hours long, and for this 

 reason it is often missed in examining the 

 animals during the periods. It is also possible, 

 as mentioned above, that the fourth stage may 

 not typically exist in all individuals and the 

 quantity of blood present is very different in 

 the different specimens. The succession in 

 which these stages follow one another is re- 

 markably definite. We have never observed 

 any change in the typical sequence of the 

 stages and the time consumed by the entire 

 process is closely the same in all cases. 



A macroscopical examination of the uterus 

 and vagina during this period of sexual activ- 

 ity shows the entire genital- tract to be con- 

 gested. The vessels to the ovary, uterus and 

 vagina are large and conspicuous, the uterine 

 horns and the vagina are slightly swollen and 

 inflamed. However, as soon as this short 

 period of activity is over, the congestion disap- 

 pears and the uterus and vagina take again 

 their normal pale aspect. At the same time 

 the vaginal fluid diminishes and the vagina, 

 especially during the first week after the sex- 

 ual activity, is as clean as jjossible, showing 

 none of the secretion. The external vaginal 

 orifice, which during the period of activity is 

 more or less open, actually showing in a few 

 cases a little fluid or some blood, closes and be- 

 comes less accessible after the period. 



During the second week following oestrus a 

 little mucous discharge begins to appear in the 

 vagina and increases progressively, indicating 

 that the new period of activity is nearer and 

 nearer approaching. The orifice of the vagina 

 is sometimes open during this stage and thus 

 explains why this sign, which was observed be- 



fore, does not make it possible to detect the 

 actual time of the regular a3strous activity. 



The complete results of the present study 

 which will be published in full elsewhere may 

 be stated in brief as follows. 



Guinea-pigs kept in a state of domestication 

 and under uniform environmental conditions 

 possess a regular dioestrous cycle repeating 

 itself in non-pregnant females about every six- 

 teen days throughout the entire year with 

 probably small and insignificant variations 

 during the different seasons. 



During each cycle typically corresponding 

 changes ,are occurring in the vagina, the 

 uterus, and the ovary; a given stage in one of 

 these organs closely accompanying parallel 

 stages in the other two. 



Each period of sexual activity lasts about 

 twenty-four hours and is characterized by the 

 presence of a definite vaginal fluid, which is 

 not sufficiently abundant to be readily de- 

 tected on the vulva, but is easily observed by 

 an examination of the interior of the vagina. 



The composition of the vaginal flviid changes 

 with the several stages of change occurring in 

 the uterus and vagina. 



(a) To begin with, during what we term the 

 first stage, the fluid consists of an abundant 

 mucous secretion containing great numbers of 

 desquamated vaginal epithelial cells. At this 

 time sections of the vagina show an active 

 shedding or desquamation of its epithelial lin- 

 ing cells. The cells of the uterine epithelium 

 are loaded with mucus, and an active migra- 

 tion of jwlynuclear leucocytes is taking place 

 from the vessels of the vagina and uterus out 

 into the stroma and towards the epithelial 

 layer. 



(6) During the second stage the contents of 

 the vagina become thick and cheese-like on ac- 

 count of the great accumulation of desqua- 

 mated epithelial cells. The walls of the uterus 

 and vagina become congested and the migra- 

 tion of leucocytes becomes still more active. 



(c) The leucocytes reach the epithelium and 

 vigorously invade its cells and intercellular 

 spaces during the tJiird stage. These wander- 

 ing cells become enclosed within and appar- 

 ently dissolve the breaking-down dead cells of 

 the epithelium. The vaginal fluid becomes 



