The semen is thus a natural stimulant, a physiological aphrodisiac, the type of a class of drugs which have been known and cultivated in all parts of the world from time immemorial. (Dufour has discussed the aphrodisiacs used in ancient Rome, _Histoire de la Prostitution_, vol. II, ch. 21.) It would be vain to attempt to enumerate all the foods and medicaments to which has been ascribed an influence in heightening the sexual impulse. (Thus, in the sixteenth century, aphrodisiacal virtues were attributed to an immense variety of foods by Liébault in his _Thresor des Remèdes Secrets pour les Maladies des Femmes_, 1585, pp. 104, et seq.) A large number of them certainly have no such effect at all, but have obtained this credit either on some magical ground or from a mistaken association. Thus the potato, when first introduced from America, had the reputation of being a powerful aphrodisiac, and the Elizabethan dramatists contain many references to this supposed virtue. As we know, potatoes, even when taken in the largest doses, have not the slightest aphrodisiac effect, and the Irish peasantry, whose diet consists very largely of potatoes, are even regarded as possessing an unusually small measure of sexual feeling. It is probable that the mistake arose from the fact that potatoes were originally a luxury, and luxuries frequently tend to be regarded as aphrodisiacs, since they are consumed under circumstances which tend to arouse the sexual desires. It is possible also that, as has been plausibly suggested, the misunderstanding may have been due to sailors--the first to be familiar with the potato--who attributed to this particular element of their diet ashore the generally stimulating qualities of their life in port. The eryngo (_Eryngium maritimum_), or sea holly, which also had an erotic reputation in Elizabethan times, may well have acquired it in the same way. Many other vegetables have a similar reputation, which they still retain. Thus onions are regarded as aphrodisiacal, and were so regarded by the Greeks, as we learn from Aristophanes. It is noteworthy that Marro, a reliable observer, has found that in Italy, both in prisons and asylums, lascivious people are fond of onions (_La Pubertà_, p. 297), and it may perhaps be worth while to recall the observation of Sérieux that in a woman in whom the sexual instinct only awoke in middle age there was a horror of leeks. In some countries, and especially in Belgium, celery is popularly looked upon as a sexual stimulant. Various condiments, again, have the same reputation, perhaps because they are hot and because sexual desire is regarded, rightly enough, as a kind of heat. Fish--skate, for instance, and notably oysters and other shellfish--are very widely regarded as aphrodisiacs, and Kisch