+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. +Contagious Recurrences or Relapses.+--The duration of the infectious period in untreated cases and the proportion of infectious lesions in a given case vary a good deal and both may be matters of the utmost importance. Some persons with syphilis may have almost no recognizable lesions after the chancre has disappeared. Others under the same conditions may have crop after crop of them. There is a kind of case in which recurrences are especially common on the mucous or moist surfaces of the mouth and throat, and such patients may hardly be free from them or from warty and moist growths about the genitals during the first five years of the disease, unless they are continuously and thoroughly treated. Irritation about the genitals and the use of tobacco in the mouth encourage the appearance of contagious patches. Smokers, chewers, persons with foul mouths and bad teeth, and prostitutes are especially dangerous for these reasons. +Average Contagious Period.+--It is a safe general rule, the product of long experience, to consider a person with an untreated[10] syphilis as decidedly infectious for the first three years of his disease, and somewhat so the next two years. The duration of infectiousness may be longer, although it is not the rule. It must be said, however, that more exact study of this matter since the germ of syphilis was discovered has tended to show that the contagious period is apt to be longer than was at first supposed, and has taught us the importance of hidden sores in such places as the throat and vagina. [10] The control of infectiousness in syphilis through treatment is considered in the next chapter. [Illustration: FRITZ SCHAUDINN [1871-1906] (From the "Galerie hervorragender Aerzte und Naturforscher." Supplement to the Muenchener med. Wochenschrift, 1906. J. F. Lehmann, Munich.)]