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.
Some of these imply direct contact—such, for example, as kissing, the digital examination of syphilitic patients by doctors or nurses, or infection of the surgeon's fingers while operating upon a syphilitic patient. In suckling, a syphilitic wet nurse may infect a healthy infant, or a syphilitic infant may infect a healthy wet nurse. In other cases the infection is by indirect contact, the virus being conveyed through the medium of articles contaminated by a syphilitic patient—such, for example, as surgical instruments, tobacco pipes, wind instruments, table utensils, towels, or underclothing. Physiological secretions, such as saliva, milk, or tears, are not capable of communicating the disease unless contaminated by discharge from a syphilitic sore. While the saliva itself is innocuous, it can be, and often is, contaminated by the discharge from mucous patches or other syphilitic lesions in the mouth and throat, and is then a dangerous medium of infection. Unless these extra-genital sources of infection are borne in mind, there is a danger of failing to recognise the primary lesion of syphilis in unusual positions, such as the lip, finger, or nipple. When the disease is thus acquired by innocent transfer, it is known as syphilis insontium.
Stages or Periods of Syphilis.—Following the teaching of Ricord, it is customary to divide the life-history of syphilis into three periods or stages, referred to, for convenience, as primary, secondary, and tertiary. This division is to some extent arbitrary and artificial, as the different stages overlap one another, and the lesions of one stage merge insensibly into those of another. Wide variations are met with in the manifestations of the secondary stage, and histologically there is no valid distinction to be drawn between secondary and tertiary lesions.
The primary period embraces the interval that elapses between the initial infection and the first constitutional manifestations,—roughly, from four to eight weeks,—and includes the period of incubation, the development of the primary sore, and the enlargement of the nearest lymph glands.
The secondary period varies in duration from one to two years, during which time the patient is liable to suffer from manifestations which are for the most part superficial in character, affecting the skin and its appendages, the mucous membranes, and the lymph glands.
The tertiary period has no time-limit except that it follows upon the secondary, so that during the remainder of his life the patient is liable to suffer from manifestations which may affect the deeper tissues and internal organs as well as the skin and mucous membranes.