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The Effect of Retarded Growth Upon the Sexual Development of Rats

Animal Nutrition Laboratory, Cornell University, Ithaca, New York

1. The oestrous behavior in the absence of mating was observed throughout life in a group of rats allowed to grow at at an unrestricted rate, in a group retarded for a considerable period at 40 gm. and then allowed to grow slowly, and in a group similarly treated after an initial weight of 80 gm. The limiting factor was that of energy in the diet.

2. The average age at the opening of the vagina is recorded, also the weight at this time, for each group.

3. The age of opening of the vagina increases with the increased severity of treatment and the weight at opening decreases. Two lines of evidence indicate that age is a more important consideration than weight in determining the time at which vaginal opening occurs.

4. Increased severity of treatment increases the age and weight interval between the vaginal opening and the occurrence of first oestrus. These two events become entirely dissociated in the retarded rats.

5. In the control rats the cessation of sexual activity is a gradual process, not abrupt as in man. It is usually irreversible.

6. Anoestrous rats tended to be heavier than rats with regular cycles.

7. Seventy-one per cent of the normal rats presented continued cornified vaginal smears at some time of their lives, while this never occurred in the two retarded groups. This is probably associated with the frequency of ovulation. Cornified rats tended to weigh less than those with regular cycles.

8. The occurrence of an oestrous smear is a very delicate indication of an increased supply of energy.

9. When more energy is supplied it is used for both growth and sexual needs; no competition is shown between these demands. But when growth has proceeded so far that all the energy available is needed for maintenance both growth and sexual activity cease.

10. The males of the 40-gm. group show a deformity of the penis, the etiology of which is discussed.

11. The bearing of 3 and 9 on the mode of action of the anterior hypophysis is discussed.