306 EDGAR ALLEN 
Stage M,. In the first half of the metoestrum, the vulva has 
usually lost most of its swelling, the orifice of the vagina still 
gapes open and is whitish, occasionally showing small granula- 
tions, the lumen is still dry, and the smear shows red cornified 
elements of the previous periods, always very numerous, and 
now bunched or caked (fig. 4). 
Stage M,. This stage is evidenced by a normal vulva and a 
tightly or partly closed vaginal opening. ‘The vaginal contents 
change as the period progresses from a pasty or viscous to 
a fluid consistency, and the smear shows polymorphonuclear 
leucocytes among the red horny elements. A few polymorphs 
and many cornified cells is an early M, stage, and a heavy leuco- 
eytic infiltration and decrease in number of the cornified cells 
is a late one (fig. 5). 
This stage then merges into D with a decrease in leucocytosis 
and the appearance in the smear of small numbers of nucleated 
epithelial cells. By standardizing the technique of smear prep- 
aration, stages O and M, are easily differentiated, although the 
basis for this division is the number and clumping rather than 
any change in the character of the cells themselves. 
The separate phases as well as the duration of the whole cycle 
show great variation under the most uniform conditions of food 
and environment. Further discussion may be postponed until 
the histological condition of the various genital organs can be 
described. 
5. ANIMALS STUDIED HISTOLOGICALLY 
A series of twenty-seven carefully timed animals was prepared 
for histological study. They consisted chiefly of four strains: 
albino, black, brown, and gray. Observations were made daily 
for a period of from three to five weeks before killing, in order 
to obtain an accurate record of the number and duration of oes- 
trous periods as an aid to the interpretation of ovarian condi- 
tions. The smear made just before killing usually followed 
the routine smear for that day by three to six hours, so that 
two observations at short intervals were available for diagnosis. 
