+Contagiousness in the Primary Stage.+—­The chancre is always contagious.  If it is covered with a dry crust, it is, of course, less so, but as soon as the crust is rubbed off, the germ-infested surface is exposed and the thin, watery discharge contains immense numbers of the organisms, especially in the first two or three weeks.  This is just as true of a chancre on the lip or chin as on the genitals.  Chancres which are in moist places, as in the mouth, or on the neck of the womb, or under the foreskin, are especially dangerous, because the moisture keeps the germs on the surface.

+Contagiousness in the Secondary Stage.+—­In the secondary period, when the body is simply filled with germs, one would expect the risk to be even greater than in the primary stage.  As a matter of fact, however, no matter how many germs there are in the body, the only ones that are dangerous to others are those that are able to get to the surface.  A syphilitic nodule or hard pimple on the hand or face is not contagious so long as the skin is dry and unbroken over it.  The sores which occur in the moist, warm, protected places, like the mouth, on the lips, about the genitals, and in the folds of the body, such as the thighs, groins, armpits, and under the breasts in women, are, like the chancre, the real sources of danger in the spread of the disease.

+Relatively Non-contagious Character of Late Syphilis.+—­The older a syphilis is, the less dangerous it becomes.  It is the fresh infection and the early years which are a menace to others.  It will be recalled that the germs die out in the body in immense numbers after the active secondary period is over, so that when the tertiary stage is reached, there is only a handful left, so to speak.  The germs in a tertiary sore are so few in number that for practical purposes it is safe to say they may be disregarded, and that for that reason late syphilis is practically harmless for others.  Just as every syphilitic runs a gradual course to a tertiary period, so every syphilitic in time becomes non-contagious, almost regardless of treatment.

+The Time Element in Contagiousness.+—­It is the time that it takes an untreated case to reach a non-infectious stage and the events or conditions which can occur in the interval, that perpetuate syphilis among us.  The chancre is contagious for several weeks, and few syphilitics escape having some contagious secondary lesions the first year.  These are often inconspicuous and misunderstood.  They may be mistaken for cold sores or the lesions about the opening of the rectum may be mistaken for hemorrhoids, or piles.  The recurrence of these same kinds of sores may make the patient dangerous from time to time to those about him, without his knowledge.  It is an unfortunate thing that the most contagious lesions of syphilis often give the patient least warning of their presence in the form of pain or discomfort.  While they can often be recognized on sight by a physician, it is sometimes necessary to examine them with a dark-field microscope to prove their character by finding the germs.  It is a safer rule to regard every open sore or suspicious patch in a syphilitic as infectious until it is proved not to be so.