. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 64 SPIROCHETES epidermis up, causing it to crack over the surface in such a way as to give the little tumor the appearance of a raspberry. Little yellow summits soon develop on the tumors, composed not of pus but of a cheesy material. Some of the pimples grow no further, but most of them become capped over with the yellow cheesy substance which catches and holds particles of dust, and thus become very dirty. These are the " yaws " from which the disease takes its name. During their formation t


. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 64 SPIROCHETES epidermis up, causing it to crack over the surface in such a way as to give the little tumor the appearance of a raspberry. Little yellow summits soon develop on the tumors, composed not of pus but of a cheesy material. Some of the pimples grow no further, but most of them become capped over with the yellow cheesy substance which catches and holds particles of dust, and thus become very dirty. These are the " yaws " from which the disease takes its name. During their formation they cause some itching, but are not painful. They reach the height of their develop- ment in 12 or 14 days and then usually begin to shrink, the dirty yellow cap, now dark colored, falling off and leaving a sound patch of pale skin. Sometimes, ^°" }?k \T^^ °^ ^^^^ however, though in less than ten per cent (After Manaon.) ' . , of cases, ulceration of the yaws takes place, but this is probably due to complicating infections. The time that the disease lasts varies greatly according to the general health and constitution of the patient. In normal mild cases it may be all over in less than two months, while in weak or sickly individuals crop after crop of yaws may appear for months or years, recurring at irregular intervals. There is some evidence also that there may be a rare tertiary stage of yaws corresponding to a similar stage in syphilis, characterized by a diseased condition of the bones of the arms and legs, ulcers, etc., though this may often be due to mixed infections with syphQis or other diseases. The disease known as gangosa, prevalent in Guam and other East Indian Islands, is thought by some to be a consequence of yaws. Yaws is very seldom a fatal disease except in young children. Like syphilis it is very contagious, but the parasites are not transmitted frona mother to baby before birth or by nursing. Treatment and Prevention. — Care of the general health of


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