[Illustration: 58. Scabies on the hand. From portfolio of Dermochromes by permission of Rebman & Co., of New York. Publishers.] The disease is a cosmopolitan one, being exceedingly abundant in some localities. Its spread is much favored where large numbers of people are crowded together under insanitary conditions and hence it increases greatly during wars and is widely disseminated and abundant immediately afterwards. Though more commonly to be met with among the lower classes, it not infrequently appears among those of the most cleanly, careful habits, and it is such cases that are most liable to wrong diagnosis by the physician. Infection occurs solely through the passage, direct or indirect, of the young fertilized females to the skin of a healthy individual. The adult, oviparous females do not quit their galleries and hence do not serve to spread the disease. The young females move about more or less at night and thus the principal source of infestation is through sleeping in the same bed with an infested person, or indirectly through bedclothes, or even towels or clothing. Diurnal infestation through contact or clothing is exceptional. Many cases are known of the disease being contracted from animals suffering from scabies, or mange. When a person is exposed to infestation, the trouble manifests itself after eight or ten days, though there usually elapses a period of twenty to thirty days before there is a suspicion of anything serious. The first symptom is an intense itching which increases when the patient is in bed. When the point of irritation is examined the galleries may usually be seen as characteristic sinuous lines, at first whitish in color but soon becoming blackish because of the contained eggs and excrement. The galleries, which may not be very distinct in some cases, may measure as much as four centimeters in length. Little vesicles, of the size of a pin head are produced by the secretions of the feeding mite; they are firm, and projecting, and contain a limpid fluid. Figures 58 and 59 show the typical appearance of scabies on the hands, while figure 60 shows a severe general infestation. The intolerable itching induces scratching and through this various complications may arise. The lesions are not normally found on the face and scalp, and are rare on the back. [Illustration: 59. Scabies on the hand. After Duhring.] [Illustration: 60. Generalized infection of Scabies. After Morrow.] Formerly, scabies was considered a very serious disease, for its cause and method of treatment were unknown, and potentially it may continue indefinitely. Generation after generation of the mites may develop and finally their number become so great that the general health of the individual is seriously affected. Now that the true cause of the disease is known, it is easily controlled.