aoe EDGAR ALLEN 
serous. As the O stage begins the epithelium may become dry, 
and then granular in the My period. As the leucocytes invade 
the masses of C cells during the M. stage, the contents of the 
lumen become pasty, then milky, and finally stringy again as 
this stage merges into the dioestrous interval. 
3. Histology of the vagina 
During the D interval the epithelium is low (three to seven 
layers), has no clear-cut basement membrane, and is freely in- 
filtrated with polymorphonuclear leucocytes. At the end of this 
interval, a basement membrane begins to be evident, mitoses 
become more frequent, new layers of cells are added, and leuco- 
cytosis ceases. In the P stage growth processes reach a maxi- 
mum which thickens the epithelium to ten to thirteen layers. 
A distinct basement membrane is present in most places. Then 
the outer three to five layers begin to degenerate, as is shown by 
their loss of affinity for cytoplasmic stains and the pyenosis of 
their nuclei. These two areas become clearly separated by the 
formation of a granular layer. This is converted into a cornified 
layer (stratum lucidum), which is not superficial as would be 
supposed, but underlies three to five layers of nucleated cells. 
As the P merges into the O stage, these superficial layers disappear 
(probably through autolysis or continued cornification) until 
the cornified layer becomes superficial, at which time oestrus is 
evident. By this time continued growth has piled up the epithe- 
lium to a thickness of twelve or thirteen cell layers under the 
stratum granulosum which first formed at about the eighth layer. 
The definition of the lower layer of the germinativum from the 
adjacent stroma is very clear-cut. As the M, period sets in the 
cornified layer begins to be delaminated and the lumen of the 
vagina is filled with fragments or masses of C cells. The base- 
ment membrane becomes thinner and mesenchymal papillae 
indent the lower layers of the epithelium. Leucocytes filter in 
from the stroma and collect in the superficial layers of the ger- 
minativum. After they have accumulated in considerable num- 
bers here, they pass on into the cornified masses in the lumen, 
stage Ms, and in a day’s time may completely dissolve them. 
