Considerable interest attaches to the observations of Metchnikoff, Roux, and Neisser, who have succeeded in conveying syphilis to the chimpanzee and other members of the ape tribe, obtaining primary and secondary lesions similar to those observed in man, and also containing the spirochæte. In animals the disease has been transmitted by material from all kinds of syphilitic lesions, including even the blood in the secondary and tertiary stages of the disease. The primary lesion is in the form of an indurated papule, in every respect resembling the corresponding lesion in man, and associated with enlargement and induration of the lymph glands. The primary lesion usually appears about thirty days after inoculation, to be followed, in about half the cases, by secondary manifestations, which are usually of a mild character; in no instance has any tertiary lesion been observed. The severity of the affection amongst apes would appear to be in proportion to the nearness of the relationship of the animal to the human subject. The eye of the rabbit is also susceptible to inoculation from syphilitic lesions; the material in a finely divided state is introduced into the anterior chamber of the eye. Attempts to immunise against the disease have so far proved negative, but Metchnikoff has shown that the inunction of the part inoculated with an ointment containing 33 per cent. of calomel, within one hour of infection, suffices to neutralise the virus in man, and up to eighteen hours in monkeys. He recommends the adoption of this procedure in the prophylaxis of syphilis. Noguchi has made an emulsion of dead spirochætes which he calls _luetin_, and which gives a specific reaction resembling that of tuberculin in tuberculosis, a papule or a pustule forming at the site of the intra-dermal injection. It is said to be most efficacious in the tertiary and latent forms of syphilis, which are precisely those forms in which the diagnosis is surrounded with difficulties. ACQUIRED SYPHILIS In the vast majority of cases, infection takes place during the congress of the sexes. Delicate, easily abraded surfaces are then brought into contact, and the discharge from lesions containing the virus is placed under favourable conditions for conveying the disease from one person to the other. In the male the possibility of infection taking place is increased if the virus is retained under cover of a long and tight prepuce, and if there are abrasions on the surface with which it comes in contact. The frequency with which infection takes place on the genitals during sexual intercourse warrants syphilis being considered a venereal disease, although there are other ways in which it may be contracted.