There is almost no literature of fact concerning the periodic function as related to the mental abilities of women. No effort had ever been made to subject this matter to study by instruments and methods of precision until very recently. Psychologists, while often stating the influence of periodicity on mental life to be fundamental and characteristic, entirely neglected to consider it when performing experiments on women subjects. In 1909 Voitsecovsky, at Petrograd, performed an experiment on six women by means of instruments of precision. He thought he found a positive result and that there was shown to be an actual influence of periodicity on certain mental functions. His conclusions are, however, largely invalidated by the fact that all his subjects knew the purpose of the experiment, and by the fact that he neglected to use, as a control, human beings not subject to the phenomenon in question. He also neglected to present his data in full, so that the reliability of his conclusions might be calculated. Two studies of this phenomenon appeared in 1914. The first was a study by Dr. A. E. Arnold, as to the effect of school work on the periodic function, and this is reported in the January number of the _American Physical Education Review_. This investigator suspected, from his experience as a physician and teacher, "that much of the incapacity claimed was fictitious," and he determined, as an experiment, to institute a regime whereby no student under his supervision would be excused periodically from mental or physical duties, except in cases where some pathological condition existed. In summing up the data he says: "So far our results show all improvement [in the health of students]." The second study, which appeared in 1914, was by the present writer. She made a prolonged and careful experimental study of twenty-three women (using as a control the records of men subjects), and failed to demonstrate any influence of periodicity on those mental abilities which she tested. These included speed and accuracy of perception, controlled association, steadiness, speed of voluntary movement, fatigability, and rate of learning. A great amount of scientific work remains to be done before any final answer of any kind can be given to the question, Does functional periodicity exercise a fundamental and characteristic influence on the intellectual abilities of women? We must answer our third question in this way: There is very little experimental evidence on which to base a reply, but the few data which we do possess show no influence, either detrimental or beneficial.