Burton advances an explanation of its origin. "The only physical cause for the practice which suggests itself to me, and that must be owned to be purely conjectural, is that within the Sotadic Zone there is a blending of the masculine and feminine temperament, a crasis which elsewhere occurs only sporadically."[47] So far as it goes, this suggestion rests upon ground admitted to be empirically sound by the medical writers we have already examined, and vehemently declared to be indisputable as a fact of physiology by Ulrichs, whom I shall presently introduce to my readers. But Burton makes no effort to account for the occurrence of this crasis of masculine and feminine temperaments in the Sotadic Zone at large, and for its sporadic appearance in other regions. Would it not be more philosophical to conjecture that the crasis, if that exists at all, takes place universally; but that the consequences are only tolerated in certain parts of the globe, which he defines as the Sotadic Zone? Ancient Greece and Rome permitted them. Modern Greece and Italy have excluded them to the same extent as Northern European nations. North and South America, before the Conquest, saw no harm in them. Since its colonisation by Europeans they have been discountenanced. The phenomenon cannot therefore be regarded as specifically geographical and climatic. Besides, there is one fact mentioned by Burton which ought to make him doubt his geographical theory. He says that, after the conquest of Algiers, the French troops were infected to an enormous extent by the habits they had acquired there, and from them it spread so far and wide into civilian society that "the vice may be said to have been democratised in cities and large towns."[48] This surely proves that north of the Sotadic Zone males are neither physically incapable of the acts involved in abnormal passion, nor gifted with an insuperable disgust for them. Law, and the public opinion generated by law and religious teaching, have been deterrent causes in those regions. The problem is therefore not geographical and climatic, but social. Again, may it not be suggested that the absence of "the Vice" among the negroes and negroid races of South Africa, noticed by Burton,[49] is due to their excellent customs of sexual initiation and education at the age of puberty--customs which it is the shame of modern civilisation to have left unimitated? However this may be, Burton regards the instinct as natural, not _contre nature_, and says that its patients "deserve, not prosecution but the pitiful care of the physician and the study of the psychologist."[50]