216 TROPICAL MEDICINE AND HYGIENE 



or thick sulphur-yellow crusts and subsiding without deep 

 ulceration or the formation of any but superficial scars. 

 The usual duration of the disease is two or three years, 

 but on the parts of the body where the 'epidermis is thick, 

 such as the soles of the feet, it may persist for much 

 longer. Destructive ulceration of the mucous surface and 

 a lupoid eruption on the face are by some considered to 

 be sequelae, and onychia may also occur. 



Geographical Distribution. As an indigenous disease it 

 was probably limited to the West Coast of Africa, to the 

 aborigines of the Malay Peninsula, possibly Ceylon, and 

 to the Pacific Islands. Introduced by the slaves into 

 the West Indies and South America, it has been firmly 

 established there for over a century. An outbreak has 

 also occurred in Assam, probably introduced by labourers 

 returning from Fiji or the West Indies. Cases are occa- 

 sionally seen in many tropical ports, and to a limited 

 extent it has spread amongst the inhabitants of such 

 ports. It does not occur on the East Coast of Africa 

 and is very rare in the central plateau. Outside the 

 Tropics it does not seem to spread. 



Clinical Course. Experimental inoculations have shown 

 that there is a period of incubation of about twenty-eight 

 days. In such experiments there need be no primary 

 sore ; a primary yaw is, however, common in accidental 

 inoculation. It may appear at the edge of an ulcer or 

 in a clean-cut wound, but is more common at or near 

 the junction of the skin and mucous membranes, such as 

 the angle of the mouth. When there is a primary 

 sore it is a raised granulomatous mass similar to the 

 subsequent eruptions. The generalized eruption may 

 appear in any part of the body and is associated with 

 febrile symptoms. Sometimes the temperature is 103 

 or 104 F. There are aching pains in the limbs, and 

 particularly in the back and loins, sometimes severe 

 enough to raise the suspicion of small-pox. The erup- 

 tion may be abundant, but in other cases there may only 

 be a few yaws limited to the lower part of the face, the chest, 



