Abstract
Conclusion
It seems likely that a chemical substance in the wheat is changed by the ultraviolet radiations. Most probably this substance directly affects the anterior hypophysis, which in turn stimulates gonad activity. If this is the case we have a new explanation of the seasonal sexual activity of the sparrow in the natural state. This interpretation, which merely shifts the emphasis from light affecting the animal to light producing a change in the diet, may well apply to the seasonal sexual development of other vertebrates as well. The results of the above experiment point to an increase of Vitamin D or some kindred substance as the specific dietary factor. Other experiments, planned to determine the exact mechanism, are in progress.
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