Here is another book dealing with the safe period as a system of birth control. It emanates from Holland. The author has collected the available periodical literature and other observations made throughout the world on this subject. He discusses the various methods of calculating the safe period, recognizing the danger of the influence of suggestion on the average layman. He feels that the method can be practiced safely only when the system is controlled by an expert for from six to twelve months before undertaking the practice regularly. While his book will be of interest to the physician, the average lay reader will find it more confusing than any other of the volumes thus far available on this subject.