VAGINAL EPITHELIUM OF GUINEA-PIG 431 
As the result of following the suggestions contained in Stockard 
and Papanicolaou’s earlier paper, the cycle in the rat was worked 
out (Long, 719) and later elaborated and verified (Long and 
Evans, ’22). Smears taken from the vagina of the rat by means 
of a small spatula were studied and correlated with sections of all 
parts of the reproductive system. By means of the smears, it 
was possible to recognize four definite stages besides the interval. 
Smears taken during the first stage contained nucleated epithelial 
cells of uniform size; during the second stage, few, large, cornified 
cells; in the third stage they were made up of a great abundance 
of cornified cells; in the fourth stage, by many leucocytes admixed 
with cornified cells. Throughout the interval between stage 4 
and stage 1, or the dioestrous pause, the vaginal fluid contained 
leucocytes with only a few epithelial cells. 
The sections revealed a cyclical growth and desquamation of 
the vaginal epithelium. The epithelium is lowest during the 
interval, increasing in thickness just before the advent of stage 1. 
One of the striking features is the occurrence, during this stage, 
of the processes of cornification not in the superficial layers but 
at a depth of almost two cells, the upper two layers of cells retain- 
ing their epithelial character, later to be shed as the cells of the 
smear of stage 1. The cornified stratum so denuded becomes 
superficial, increases in thickness, and is later detached, thus 
furnishing the cells of stages 2 and 3. Leucocytes, of which the 
epithelium is devoid during stages 1, 2, and 3, now invade the 
mucosa and escape into the lumen in stage 4. 
Long and Evans attempted to correlate the cycles in the rat 
with the cycles in the guinea-pig as found by Stockard and 
Papanicolaou and as observed by themselves in twenty-two 
guinea-pigs for a couple of months. In a section of the vagina 
of the one guinea-pig which they killed, Long and Evans ob- 
served what they believed to be the cornified layer under a layer of 
epithelial cells. Since they found that such a condition occurred 
regularly in the rat, they conjectured that an epithelial layer 
superficial to the cornifying layer must be normal in the guinea- 
pig, and if such a condition were true, then it was evident that 
Stockard and Papanicolaou had overlooked it. 
