It would be impossible, in an essay of this kind, to review the whole mass of medical observation, inference and speculation which we have at our command. Nor is a layman, perhaps, well qualified for the task of criticism and comparison in a matter of delicacy where doctors differ as to details. I shall therefore content myself with giving an account of four of the most recent, most authoritative, and, as it seems to me, upon the whole most sensible studies. Moreau, Tarnowsky, Krafft-Ebing and Lombroso take very nearly similar views of the phenomenon; and between them they are gradually forming a theory which is likely to become widely accepted. _Des Aberrations du Sens Génésique, par le Dr. Paul Moreau_, 4th edition, 1887. Moreau starts with the proposition that there is a sixth sense, "le sens génital," which, like other senses, can be injured psychically and physically without the mental functions, whether affective or intellectual, suffering thereby. His book is therefore a treatise on the diseases of the sexual sense. These diseases are by no means of recent origin, he says. They have always and everywhere existed. He begins with a historical survey, which, so far as antiquity is concerned, is very defective. Having quoted with approval the following passage about Greek society:-- "La sodomie se répand dans toute la Grèce; les écoles des philosophes deviennent des maisons de débauche, et les grands exemples d'amitié légués par le paganisme ne sont, pour la plupart, qu'une infâme turpitude voilée par une sainte apparence": having quoted these words of Dr. Descuret, Moreau leaves Greece alone, and goes on to Rome. The state of morals in Rome under the empire he describes as "une dépravation maladive, devenue par la force des choses héréditaire, endémique, épidémique." Then follows a short account of the emperors and their female relatives. "Cet éréthisme génésique qui, pendant près de deux siècles, régna a l'état épidémique dans Rome" he ascribes mainly to heredity. Of Julia, the daughter of Augustus, he says, "Peut-on lutter contre un état morbide héréditaire?" The union of unrestrained debauchery and ferocity with great mental gifts strikes him as a note of disease; and he winds up with this sentence: "Parmi les causes les plus fréquentes des aberrations du sens génital, l'hérédité tient la première place."