1. It is well known that vitamin A deficiency in the young animal checks growth and results in stunting for the period of the deficiency. Such animals, however, resume growth and reach the normal adult weight when put on to a complete diet.

2. Animals in this dwarfed condition, weighing 70 to 90 gms. only at 3 to 5 months old, are quite sterile. Histological examination of the gonads and secondary organs, however, revealed in most cases no anatomical reason for their sterility. Gametogenesis was found to be in progress in these stunted animals, and the accessory organs appeared to be normal.

3. It was concluded, therefore, that the sterility was due, primarily to physiological debility and disinclination to copulate.

4. That this was actually the case was shown by a further batch of deficiency animals which were reciprocally mated with each other and with normals, daily examinations being made for evidence of copulation. None of the females copulated, but one only slightly deficient buck copulated with a normal doe. At the same time, however, vaginal smearing showed that the cyclic activity in the female genital organs, associated with the cestrous cycle, occurred in the deficient females.

5. When normal weight is attained after recovery on natural diets breeding takes place freely, and fertility and sexratio show no marked abnormality.

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