1. The growth .energy of the granulosa cells in the ovarian follicles of normal guinea pig ovaries varies with the size of the follcle, and follows a definite growth curve. The growth energy in small follicles is relatively low, then a gradual rise takes place with increase in size of the follicle up to a maximum which is reached when the follicle attains medium size. This ascending part of the curve is followed by a gradual fall in growth energy until in large follicles the proliferative power has fallen almost to the level of small follicles. Synchronously with maturity of the follicles there is an abrupt fall in growth energy to near the zero point.

2. There is a distinct localization of mitoses in the follicle. The large majority of mitoses is found in the perioval part. With increase in the growth energy which characterizes medium follicles, there is an increase in the proliferative power of the cells more distal to the egg, but still near the egg. We may therefore conclude on the basis of our observations and on the previous observations of Loeb, that the egg exerts a stimulus, which causes proliferation of the granulosa cells.

3. Under pathological conditions certain changes occur in the growth energy of the follicle: (a) Granulosa degeneration causes in the living cells a diminution in the proliferative power which is proportionate to the extent of the degeneration. (b) Hypotypical follicles have approximately the same or only slightly diminished proliferative power as normal ones, and thus their failure to grow is essentially due to disintegration of the granulosa cells.

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