DISINFECTION ,. 31 



is " infectious material," in the sense in which we 

 use these words ; that is, they do not, so far as we 

 know, give rise directly to any infectious disease. 

 Indirectly they are concerned in the extension of the 

 " filth diseases," such as cholera, bubonic plague, and 

 typhoid fever. This because persons exposed to the 

 foul emanations from sewers, privy vaults, and other 

 receptacles of filth have their vital resisting power 

 lowered by the continued respiration of an atmo- 

 sphere contaminated with these poisonous gases, and 

 are liable to become the victims of any infectious dis- 

 ease to which they may be exposed. 



