THE OESTROUS CYCLE IN THE MOUSE ane 
Their continued action in the superficial part of the germina- 
tivum reduces these layers to the appearance of a reticulum 
containing large clumps of leucocytes. This process gradually 
declines until the vaginal epithelium returns to a typical dioes- 
trous condition (figs. 6 to 13). 
Growth activity seems practically at a standstill in the early 
D stage. Toward the end of this interval the growth curve 
begins to rise until it attains its maximum in a late stage P, after 
which it gradually falls during O and M, to its minimum in the 
late M. and early D stages. 
4. The uterine changes — 
Although the uterus goes through a cycle of changes, they 
are far less striking than those occurring in the vagina. Gross 
changes consist of a marked hyperemia and distention during 
‘the P stage, which diminishes gradually during oestrus and disap- 
pears as the M, period progresses. During the D interval the 
uterus is anemic. 
Histological changes in the uterus consist of periodic growth, 
degeneration, and leucocytosis of the epithelial cells. These 
phases coincide with those in the vagina. A hyperfunction of 
the uterine glands (judged by the distention of their ducts) is the 
evident cause of the distention of the uterine cornua during the 
P and O stages, at which time they are very transparent. Uterine 
glands are distributed everywhere throughout the uterine mucosa 
except along the line of attachment of the broad ligament. The 
glandular epithelium escapes much of the degeneration and 
destruction common to the other epithelial tissues. Mitoses 
are most frequent in the glands during the late D and early P 
stages, becoming less in number as functional activity increases. 
In other words, the growth wave in the glands slightly precedes 
that in the uterine and vaginal epithelium. 
The shape of the uterine epithelial cells varies chiefly with the 
degree of distention of the cornua, and is consequently a poor 
criterion of growth. Degenerative processes are first apparent 
in this tissue in the fading of the basement membrane (which is 
so clear-cut during the P and O stages) into a pink-staining 
