408 DISSERTATION OX THE YAWS. 



that it is a poison of a peculiar kind, which, when once it gets 

 into the habit, produces certain effects. Nor has it been well 

 ascertained what length of time is requisite from the receiving 

 the contagion to the appearance of the yaws. If any experi- 

 ments have been made, the result has not come to my know- 

 ledge. 



There is no other mode of communicating the yaws but by 

 inoculation, or the application of the ichor from the sores of 

 the infected to the wounds, ulcers, or excoriations of people 

 otherwise in health. Some will resist the action of variolous 

 contagion, even by repeated inoculation ; but no habit, age, 

 sex, or Country, is proof against the contagion of the yaws 

 once in his lifetime. 



There are several ways by which the yaws may be con- 

 tracted ; 1st, By sleeping in the same bed, and the ichor 

 from the yaws getting on wounds or scratches of the unin- 

 fected ; %dly, By handling the infected, and allowing the virus 

 to touch scratches or excoriations ; 3dly, Let us suppose (and 

 in fact it often happens), that a Negro is admitted with a 

 sore on his leg, into the hot-house or infirmary on an estate, 

 for cure, and the state of the ulcer is not attended to, till 

 some time afterwards it turns out to be the yaws. Other 

 Negroes, with common sores, will often wash their sores in 

 the same bowl or basin ; and if so, they will assuredly receive 

 the contagion ; ithly ', But the most common way this infec- 

 tion is propagated, is by small flies, who, gorging themselves 

 with the ichor of the infected, alight on the ulcers, &c. of 

 those who never had the disease ; and, however minute the 

 quantity thus applied, it will as effectually occasion the disease, 

 as if put on in abundance. 



Ratio Symptoniatum.— -To account for the various phe- 

 nomena in contagious diseases, and particularly those of 

 the eruptive kind, seems difficult, and even impossible 



