In a previous paper (published in January, 1904, in the _Annales de l’Institut Pasteur_) Sabouraud had proposed a method of treating ringworm with X-rays, which he sums up as follows: “The application in one sitting upon a given point of the scalp of a quantity of X-rays equal to 4-1/2-5 H-units of Holzknecht is made; fifteen days later a complete epilation will occur on the region treated, healthy as well as diseased hairs being shed. New and healthy hair will commence to grow ten weeks after the treatment, and will be completely restored within ten weeks. The infectivity of the disease will cease with the fall of the last diseased hair, within twenty-five days at latest of the treatment.” This formula, Sabouraud maintains, has been amply proved to be true by his experience of the six months which have intervened since his paper of January, 1904. Some very striking results are quoted. Thus while in six months before this treatment was adopted 57 patients were discharged as cured, in the past six months 134 such patients were discharged; moreover, a very large number of patients were treated without admission and also cured. An entire section of the hospital, consisting of one hundred beds set apart for favus cases, has been closed and will be converted to the uses of general medicine, as being no longer required for its former purpose. Certain additional knowledge has been afforded by the experience of the past six months, which may be stated in the following practical rules: The penetration of X-rays is proportional to their number; the more penetrating they are, the more numerous they are. The danger of X-rays is proportional to their penetration; it is thus more dangerous to handle X-rays of 8°-11° (on Benoist’s radio-chromometer) than rays of 3°-5°. Now tubes change progressively with use and these changes are marked by colour changes in the glass. At first, after about ten hours’ use, the tubes take a violet coloration; with this there is no impairment of function. But with further use, after about thirty hours, a brown tint becomes marked, and the tube is said to be “smoked.” With this change it becomes increasingly difficult to obtain rays of a low degree of penetration. For epilation rays of all degrees of penetration serve equally well; rays of 3° are as effective as rays of 11°, but the treatment must be for a longer time. Thus a tube working at 3° caused an epilation in twenty-five minutes. The same epilation would result in eleven minutes from a tube at 8°-11°; and if one used the latter tube for twenty-five minutes, a dermatitis would result. This is entirely unnecessary for epilation and is attended by mischievous consequences, even when quite slight, and must be avoided. All forms of dermatitis, except that of transient erythema, produce permanent baldness. Permanent alopecia may also result without dermatitis in cases where the amount of X-rays given has been insufficient to cause epilation, and a second