The general course of the disease is as follows. Previous to the eruption there may or may not be any disorder of health; in children (who form a large part of the subjects of yaws) there will probably be rheumatic pains in the limbs and joints, with languor, debility, and upset of the digestion; in adults of ordinary vigour the eruption is often the first sign, and it is attended with few or no constitutional troubles. The eruption begins as small pimples like a pin’s head, smooth and nearly level with the surface; they have a little whitish speck on their tops, grow rapidly, and reach the size of a sixpence or a shilling. The pustules then break, and a thick viscid ichor exudes and dries upon them as a whitish slough, and around their base as a yellowish brown crust. Beneath the whitish slough is the raspberry excrescence or yaw proper, a reddish fungous growth with a nodular surface. The favourite seats of the eruption are the forehead, face, neck, armpits, groin, genitals, perinaeum, and buttocks. Hairs at the seat of a yaw turn white. In young children or infants the corners of the mouth ulcerate, as in syphilis, and the perineal excrescences resemble condylomata. The pustules and excrescences do not all arise in one crop: some are found mature while others are only starting. If the patient be of sound constitution and good reaction, the yaws may reach the full size of a mulberry in a month, in which case they will probably be few; but in persons of poor health they may take three months to attain the size of a wood-strawberry, in which case they will be numerous inversely to their size. Often there is one yaw much larger than the rest, and longer in falling; it is called the “master yaw” or “mother yaw.” On the soles of the feet (less often on the palms of the hands) the bursting yaws are as if imprisoned beneath the homy cuticle; they cause swelling and tenderness of the foot, until set free by paring the callous skin down to the quick; these yaws are called “crab yaws” or tubbas. Usually a yaw is painless unless when rubbed or irritated. The absence of pain is used as a diagnostic sign if there be any doubt as to the nature of the attack: a pustule is opened, and a little of the juice of capsicum dropped into it; if it be a yaw, no smarting will be felt. In some cases a few yaws will show themselves long after the primary attack is over; these are called “memba yaws” (from “remember ”), the term being sometimes applied also to protracted cases with successive crops of eruption. Six weeks is the average time in a good case, from the first of the eruption to the fall of the excrescences; in such regular cases a scar remains, it may be for many months, darker than the rest of the (Negro) skin. But the disease is often a much more tedious affair, the more protracted type having become common in the West Indies of recent years. In such cases the eruption comes out by degrees and as if with difficulty, crop after crop; foul, excavating, and corroding ulcers may remain, or a limb may be in part seamed and mutilated by the scars of old ulceration. The scars after ulceration are not so dark as the skin around.

That yaws is a communicable disease is beyond question; but that.it has always arisen by conveyance of yawey matter from a previous case is neither proved nor probable. Being to a great extent a disease of childhood, it is not usually conveyed after the manner of syphilis, but by contact in other ways (as in the epidemic syphilis of 1494-1520 and in recent circumscribed epidemics). An abrasion or wound of the surface, such as a chigoe bite or a cut of the foot, is a likely point of entrance for the virus. If the yawey matter finds access to a pre-existing sore or ulcer, it causes the latter to take on a foul and sloughing condition. No sore or yaw is induced at the point of infection, which will probably be healed long before the eruption appears. It is said, however, that the pustules appear earliest and in greatest numbers on the skin near the spot where the virus entered. They follow the infection at an interval of several weeks (incubation period). Cases of yaws by infection are not unknown in white persons of good position, both children and adults, in the West Indies and elsewhere.

The nature of the disease is obscure. It is alleged to be hereditary by some, and denied to be so by others; the fact seems to be that some constitutions are much more susceptible than others, and susceptible at some periods or states of health more than at others. As an epidemic, the disease in a locality has seasons of activity and quiet. One attack in childhood gives a large degree of immunity for the rest of life. Yaws used to break out in the slaves on board Guineamen. Both in Africa and among the slaves in the West Indies it was a custom to inoculate the yaws, so as to get the attack over (called “buying the yaws”) or to get put upon the sick list.

As regards treatment, the malady in a person of good constitution runs its course and gets well in a few weeks. Whatever tends to check the eruption, such as exposure to chill, is to be avoided. A week’s course of cream of tartar and sulphur (confection of sulphur) at the beginning of the illness is often resorted to, so as to bring the eruption well out. The patient should remain indoors, in a well-aired room, and take daily warm baths and diluent drinks. If the excrescences are flabby and unhealthy, it is an indication for generous diet. Mercurial treatment is no longer in vogue. As external applications, weak lotions of zinc or carbolic acid may be used, and, if the excrescences are irritable, a watery solution of opium. Tedious and unhealthy yaws should be dressed with a wash of sulphate of zinc or of copper; the same may be applied to a yaw ulcer. The crab yaws of the horny soles or palms, after they are let through by paring the cuticle, may be dusted with alum powder. The most intractable cases occur in badly nourished and anaemic subjects, and these will often go on for months in hospital without mending. Of late in the West Indies the disease has become largely a morbus miseriae, and to that extent less amenable to treatment.

The date of the first appearance of yaws in the West Indies and Brazil is matter of dispute; the general belief is that it came in with the African Negro. After the emancipation in 1838 there was a marked decline in the prevalence of the disease in Jamaica and other colonies. In Jamaica it began to be seen again from 1854 to 1864, the cases being more of adult age than formerly. The worst recent centre of yaws has been Dominica, which is occupied by Negro communities unprovided with medical attendance. In 1871 the Government opened and maintained two special hospitals for yaws (under a board of commissioners), one at Morne Bruce near Roseau, and the other at Prince Rupert’s. In Barbados and Antigua cases of yaws are rarely seen, the population being more creole than Negro. Trinidad has a good deal of the disease from time to time in the inland villages; bad cases are admitted to the leper asylum at Port of Spain. In Grenada, which has a special yaws hospital, and in St Vincent the immigration of Hindu coolies received a check owing to the ravages made by the disease among them. It prevails also in San Domingo, Guadeloupe, and others of the Antilles. At Berbice and Essequibo there were 23 fatal cases in one year (1870). The disease is common in all parts of Brazil. In western Africa cases are found along the whole coast from the Senegal to the Congo, and in the interior (Timbuktu and Bornu). On the East Coast it is found in Mozambique, Madagascar, and the Comoros Its localities in the East Indies and islands of the Pacific have been already mentioned.

For the literature dealing with the subject, see Hirsch, Geographical and Historical Pathology (Engl. trans ), vol. ii., London, 1885 (New Sydenham Soc.).