"These are the only cases with which I am personally and intimately acquainted. But no one can have passed through a public-school and college life without constantly observing indications of the phenomenon in question. It is clear to me that in a large number of instances there is no fixed line between what is called distinctively 'friendship' and love; and it is probably the influence of custom and public opinion that in most cases finally specializes the physical passion in the direction of the opposite sex." The classification of the varieties of homosexuality is a matter of difficulty, and no classification is very fundamental. The early attempts of Krafft-Ebing and others at elaborate classification are no longer acceptable. Even the most elementary groupings become doubtful when we have definitely to fit our cases into them. The old distinction between congenital and acquired homosexuality has ceased to possess significance. When we have recognized that there is a tendency for homosexuality to arise in persons of usually normal tendency who are placed under conditions (as on board ship or in prison) where the exercise of normal sexuality is impossible, there is little further classification to be achieved along this line.[129] We have gone as far as is necessary by admitting a general undefined homosexuality,--a relationship of unspecified nature to persons of the same sex,--in addition to the more specific sexual inversion.[130] It may now be said to be recognized by all authorities, even by Freud who emphasizes a special psychological mechanism by which homosexuality may become established, that a congenital predisposition as well as an acquired tendency is necessary to constitute true inversion, apparent exceptions being too few to carry much weight. Krafft-Ebing, Näcke, Iwan Bloch, who at one time believed in the possibility of acquired inversion, all finally abandoned that view, and even Schrenck-Notzing, a vigorous champion of the doctrine of acquired inversion twenty years ago, admits the necessity of a favoring predisposition, an admission which renders the distinction between innate and acquired an unimportant, if not a merely verbal, distinction.[131] Supposing, indeed, that we are prepared to admit that true inversion may be purely acquired the decision in any particular case must be extremely difficult, and I have found very few cases which, even with imperfect knowledge, could fairly so be termed.