64 LEO LOEB 
SUMMARY 
The principal result of our investigations we can state as follows: 
In the ovary of the guinea pig (and probably of mammals gener- 
ally) cyclic changes take place independently of copulation and of 
pregnancy. 
A sexual period (the period between two ovulations) is accom- 
panied by a series of changes in the follicles. As a result of the 
conditions leading to or accompanying ovulation the granulosa 
of all large and medium follicles undergoes a very rapid degenera- 
tion, which is very marked within an hour or two after ovulation, 
or perhaps even sooner. In the follicles in which the cavity is as 
yet very small, the degenerative processes are very slight or absent. 
These follicles do not seem to perish. These degenerative changes 
affect equally both ovaries of one animal, even if a rupture of 
follicles should have taken place in only one of the two ovaries. 
The local effect of the rupture of the follicle can therefore not be 
the cause of the follicular degeneration. Within the next few 
days the small follicles grow and gradually attain a large size. 
Eight days after ovulation large follicles are again noticeable. 
As soon as good sized and medium sized follicles have been formed 
they begin to undergo degenerative processes, the granulosa 
degenerating and becoming dissolved and connective tissue grow- 
ing into the follicular cavity. This process ends in an almost 
complete disappearance of these follicles. In the meantime other 
follicles grow and, having reached a large size, they also degenerate. 
Thus after a first stage of general growth, comprising approxi- 
mately ten days after ovulation, a certain equilibrium is reached in 
which new follicles are growing to a certain size, and in which other 
follicles of large or medium size degenerate. Whether certain quan- 
titative differences in the proportion of the number of growing and 
degenerating follicles exist at different periods of this second part of 
the sexual cycle, will still have to be determined. This second 
period of equilibrium begins approximately ten days after the last 
ovulation, and it lasts until a new ovulation occurs. Gradually a 
few large follicles undergo still further changes, the cytoplasm of 
their granulosa cells enlarges, the number of mitoses in these 
