The conscientious practitioner of medicine, too, will gladly add to the scanty, though accurate, knowledge of the sex-instinct and its pathology which is all that even the best medical course can compass, the facts presented by a specialist in this field. The easiest way for those parents who accept the responsibility for rational guidance of their children in matters of sex-behavior to discharge this responsibility is by the aid of the family physician. For the physician in such cases to gain the child's confidence, understand his individual dangers and possible false attitudes, and give more than perfunctory general counsel, knowledge of the psychology of sex-behavior, as well as its physiology, is necessary. In general, also, modern medical practice must look after the _prevention_ of bad habits and unnecessary anxieties in respect to the sex-life as well as their cure; and the science of preventive medicine in this field receives a substantial contribution from this summary of the sex-life of childhood. There are now many men and women who are dissatisfied with doing for their children merely what outgrown customs decree, who are willing to give time and study, as well as money and affection, in their service, and who are eager to see or hear or read anything pertinent to their welfare. For many such parents, if they are of the scientific, matter-of-fact type, Dr. Moll's book may prove the means of answering many troublesome questions and of prompting to a wiser cooperation with church, school, and the medical profession in safeguarding their own--and, we may hope, all other--children against blunders and contaminations. One word of caution is perhaps necessary for those readers who are unused to descriptions of symptoms of diseases, abnormalities, and defects. Such readers are likely to interpret perfectly ordinary facts as the symptoms which they have been studying. So the medical student at the beginning of his reading, fears appendicitis when he has slight indigestion, and sees incipient tuberculosis in every household! So the embryonic psychologist finds 'degenerates' in every crowd of boys, 'hypnotic suggestion' in every popular preacher, and 'aphasia' in any friend who forgets names and faces! Dr. Moll gives more protection against such exaggerated inferences than is commonly given in books on pathology, but many of his readers will do well to be on their guard lest they interpret perfectly innocent behavior as a symptom of abnormality. The mischief done by our present ignorance and neglect of important features of sex-behavior should be prevented without the incidence of mischief from exaggerated expectations and unwise meddling.