CYCLIC CHANGES IN THE OVARY OF GUINEA PIG 45 
atresia. Similar conditions are found in other ovaries at the same 
period. 
Twenty-two hours after copulation some granulosa cells are 
found degenerated even in small follicles, (follicles having a small 
cavity); these degenerated granulosa cells are dissolved. 
Similar changes take place in ovaries of guinea pigs in which 
ovulation followed delivery. In a guinea pig in which copulation 
took place two hours after delivery and in which the ovaries were 
examined seventeen hours after copulation, only a few quite small 
follicles without granulosa degeneration were found; in the large 
and also in the medium sized follicles much granulosa degenera- 
tion had taken place, the central granulosa cells degenerating 
first. Almost no entirely good follicles were left. As soon as the 
interna becomes exposed, phagocytic cells (rounded off interna 
cells) penetrate into the follicular cavity and these cells take up 
debris of the granulosa. The degeneration of the granulosa cells 
is as usual followed by ingrowth of connective tissue. 
In other ovaries the granulosa may be degenerated to a great 
extent, but some remnants may still be left. Especially the 
granulosa cells of the discus proligerus survive usually the rest of 
the granulosa. We find of course various stages of connective 
tissue atresia besides the degeneration of the granulosa. From 
these observations it follows that the onset of degeneration of the 
granulosa must be extremely rapid. 
If we extirpate the corpora lutea, from two to eight days after 
copulation a new spontaneous rupture of follicles takes place in 
most cases approximately from thirteen to fifteen days after the 
previous ‘copulation, even if the female had been kept entirely 
isolated during the whole period following the extirpation of the 
corpora lutea. This early spontaneous ovulation is accompanied 
by the same follicular degeneration which we described above. 
It is an interesting problem, whether an artificially produced 
rupture of a follicle, with the subsequent development of a corpus 
luteum, is accompanied by the same acute follicular degeneration. 
Several years ago we made experiments in which we pricked or cut 
the surface of ovaries of guinea pigs which were either ‘in heat,’ 
without however having copulated, or which copulated a few hours 
previously, or which had in some cases copulated from three to six 
