AND MARSHY SITUATIONS. 139 



has been expofed in fuch fituations. It was a concur- 

 rence of thefe circumftances which gave origin to the 

 yellow fever which appeared in Grenada in the begin- 

 ning of the year 1793, and which was afterwards im- 

 ported into Philadelphia, as appears from the account 

 publifhed by Dr. Chifhohn.* 



Noxious effluvia indeed frequently arife from putrid 

 animal fubftances in confined fituations. Dr. Monro 

 mentions a remarkable inftance of this, and fome later 

 examples are recorded by Mr. St. John ; but it does not 

 appear from thefe cafes that thofe noxious effluvia pro- 

 duced any fymptoms, refembling thofe of putrid or pefti- 

 lential fevers ; on the contrary they adled as direct flimu- 

 lants, and occafioned inflammatory affections without 

 being preceded by that fenfe of debility which always 

 precedes thofe fevers that are occafioned by febrile 

 contagion. 



Having now fliewn, that the difeafes which prevail 

 moft generally during the autumnal feafon in low and 

 marfhy fituations, owe their origin, not to invifible ex- 

 halations or miafmata, but to the caufes which 1 have 

 affigned, the prophylaxis, or the means of preventing 

 the occurrence of thofe difeafes mull; be iimple and 

 obvious. 



Thefe are to introduce and increafe the proportion of 

 oxygenous gas in the fuperincumbent atmofphere, and 

 to prevent its future abftradion, by cutting off or dimi- 

 nifhing the fources of putrefa<£lion. 



It would be a happy circumilance if the application 

 of the means fuited to produce an amendment in a body 

 fo large and fludluating as the atmofphere, was as pradli- 

 cable as the means fuited to effedt that purpofe are ob- 

 vious : but unfortunately, this requires too much labour 

 and expence to admit of extenfive application, efpecially 



* Vide Chilholm's Efiay on the fever of Grenada in 1703 &c. 



iu 



