=Location of Primary Lesions.=--Owing to the greater delicacy of the mucous membranes they are more frequently the site of primary lesions than the skin: 85 to 90 per cent. of all primary sores occur about the genitalia; in men, especially on the inner side of the prepuce, the glands, and the sulcus behind it; externally, chancre may occur upon any part of the surrounding skin; in women, the tissues about the vulva are most frequently its seat. Occasionally it is found within the vagina, but rarely upon the os. The so-called extragenital chancres are met with anywhere, especially on the most exposed parts, as the lips, tongue, tonsils, eyelids, and nipples. Syphilis is occasionally conveyed to a wet-nurse by the infected mouth of an infant suffering from hereditary disease; even multiple chancres sometimes occurring. Conversely, children have been infected by wet-nurses with syphilitic lesions about the nipple. The disease has been conveyed by bites, as upon the face and fingers. Surgeons and obstetricians are peculiarly exposed, as are also nurses, to this disease, especially occurring upon the fingers and hands. Infants have been known to be inoculated during parturition. These are all examples of _direct_ or _immediate_ contagion. On the other hand, the disease may be positively conveyed by utensils in common use between different individuals, as table-ware or tobacco-pipes; by tools of trade which are passed from one person to another, as, for instance, the blowpipe in glass factories; and by cigars as they are made in some places, the wrapper being moistened from the mouth of the cigarmaker. These are examples of its _indirect_ transmission. Physicians are familiar as well with instances where the disease has been conveyed by instruments, either surgical or those of the dentist. So possible is this last form of contagion that dentists are trained to sterilize their instruments as carefully as does the surgeon. Possibility of conveying syphilis by vaccinal lymph has been alluded to as occurring only in those instances where the blood of the syphilitic patient is mingled with the lymph. The production of vaccinal virus is now, however, so well regulated that it is rare that the surgeon employs humanized lymph. Some cases considered vaccinal have been due to the _use of infected instruments_; hence the necessity for extreme caution in this regard. When the disease is acquired in a non-venereal manner it is called _syphilis insontium_, or syphilis of the innocent; this, however, is an unfortunate expression, as it tends to cast reflections upon other cases which may be, in effect, just as innocent.