46 LEO LOEB 
days previously. In only one case did we find a young corpus 
luteum the origin of which could reasonably be attributed to the 
cutting of the ovary and to the artificial rupture of a follicle. 
In this case an animal had been used which showed the first symp- 
toms characteristic for the period of heat. Three days after the 
cuts had been made the ovaries were examined. One young 
corpus luteum was found in the cortex of the ovary. Blood and 
connective tissue were found in the center of the corpus luteum; 
connective tissue and vessels grew into the corpus luteum, which 
was very small. In this ovary we found good follicles of small 
medium and large size; we also found large follicles with begin- 
ning and with further advanced granulosa degeneration, and with 
beginning ingrowth of connective tissue. In as much as in no 
case of spontaneous rupture the follicles were found in a similar 
condition at that period after the rupture, it is very probable that 
we have in this case to deal with an artificial rupture of follicles and 
that such an artificial rupture of follicles 1s not accompanied by the 
rapid degeneration of the follicular granulosa. 
On the basis of our previous results we can easily understand, 
why in all probability we succeeded in one case only in causing an 
artificial rupture of a follicle. Suchanexperiment does not promise 
to be successful, unless we have the chance of opening a mature 
follicle, and such an opportunity exists only at periods of very 
short duration. 
In these ovaries we find usually two or three generations of cor- 
pora lutea; namely: 
1. The young corpora lutea, developing in the recently rup- 
tured follicles. These corpora lutea we have described elsewhere 
in their development up to the sixth day. 
2. Corpora lutea that had formed at the time of the preceding 
ovulation, which had not been followed by pregnancy in female 
guinea pigs which had been kept separated from males. These 
corpora lutea are therefore in all probability approximately nine- 
teen to twenty-eight daysold. They show signs of beginning retro- 
gression. Their lutein cells are more or less vacuolar, especially 
in the periphery, where the vacuolization usually begins; gradually 
the vacuolization progresses to the central part. In the center of 
