352 THE LAWS OF ORGANIC 



they are more frequently attacked than others 

 similarly constituted, in the same situations. In 

 agricultural pursuits there are pure air and exer- 

 cise ; but when those who follow such pursuits re- 

 side in, or visit a town, for a period, however 

 short, where fever is raging, they not unusually 

 become affected. We must, in the first place, 

 suppose a specific poison to exist in the atmos- 

 phere to which the patient is confined, and to 

 which every person is equally exposed that 

 approaches its limits ; but, besides this, there is 

 an unhealthy condition of the air which is 

 breathed, arising from its deficient circulation 

 and from want of cleanliness, to which one 

 unaccustomed to such impurities is more par- 

 ticularly sensible. This state of the atmos- 

 phere acts conjointly with the contagious mat- 

 ter; but that is particularly felt by him only 

 who is a stranger to its qualities, and, therefore, 

 it is obvious that he has to contend against this 

 condition of the atmosphere, and also against the 

 common specific principle of the disease* 



CCCCXXI. Professional characters, for the 

 purpose of investigating truth, or relieving the 

 sick, have occasionally devoted their days and 

 nights to attendance on those suffering under the 

 most severe forms of the plague, without falling 

 a sacrifice to its ravages. To him who is fully 

 acquainted with history, it is superfluous to men- 

 tion many remarkable instances connected with 



* Vide Appendix. 



