188 



biy ternary or quaternary combinations of azof, 

 phosphorus, hydrogen, carbon, and sulphur. 

 A five-hundredth part of sulphuretted hydrogen 

 mixed with atmospheric air is sufficient, to as- 

 phyxiate a dog ; and the present state of eudio- 

 metry does not afford us means of appreciating 

 gaseous mixtures, which are more or less hurt- 

 ful to health, according as the elements in in- 

 finitely small quantities combine in different 

 proportions. One of the most important ser- 

 vices, that modern chemistry has rendered to 

 physiology, is it's having taught us, that we are 

 still ignorant of what illusory experiments on 

 the chemical composition and salubrity of the 

 atmosphere had led us to admit fifteen years 

 ago. 



The situation of the Laguna of Campoma ren- 

 ders the north-west wind, whch blows frequent- 

 ly after sunset, very pernicious to the inhabi- 

 tants of the little town of Cariaco. It's in- 

 fluence can be the less doubted, as intermit- 

 ting fevers are seen to degenerate into typhoid 

 fevers, in proportion as we approach the Laguna, 

 which is the principal focus of putrid miasmata. 

 Whole families of free negroes, who have small 

 plantations on the northern coast of the Gulf of 

 Cariaco, languish in their hammocks from the 

 beginning of the rainy season. These inter- 

 mittent fevers assume a dangerous character 

 when persons, debilitated by long labour and 



