OF NiTURAL HISTORY. l35 



The vicinity of marfhes, of ftagnating waters, of manufac- 

 tures of tallow, oil, fal ammoniac, the fmelting or corroding 

 of metals of every kind, and many other operations which 

 contaminate the air, fhould be either avoided or removed, 

 as they are the pefts of our fenfes, and the poifoners of our 

 conftitutions. Even in northern climates, houfes furrounded 

 with trees, or in the neighborhood of luxuriant vegetables, 

 are always damp, and infefted with infefls ; and hence the 

 ambient air is replete with the feeds of difeafe. Precautions 

 pf this kind are ftill more necefTary in hot climates. Air, 

 like other menftruums, abforbs a greater or lefs proportion 

 of the particles of bodies, according to its degree of heat. 

 In Madrid, however, in Conftantinople, and in many other 

 cities of warm regions, the houfes are crouded together, the 

 ftreets are narrow, and covered with filth of every kind. We 

 cannot, therefore, be furprifed, that human beings exifting in 

 fuch fituations iJbould be fo frequently infeded with peftilen* 

 tial difeafej* 



