THEIR MODE OF ACTION. 377 



Ammonia is very generally produced in cases of 

 disease ; it is always emitted in those in which con- 

 tagion is generated, and is an invariable product of 

 the decomposition of animal matter. The presence 

 of ammonia in the air of chambers in which diseased 

 patients lie, particularly of those afflicted with a 

 contagious disease, may be readily detected ; for 

 the moisture condensed by ice in the manner just 

 described, produces a white precipitate in a solution 

 of corrosive sublimate, just as a solution of am- 

 monia does. The ammoniacal salts also, which are 

 obtained by the evaporation of rain water after an 

 acid has been added, when treated with lime so as 

 to set free their ammonia, emit an odour most 

 closely resembling that of corpses, or the peculiar 

 smell of dunghills. 



By evaporating acids in air containing gaseous 

 contagions, the ammonia is neutralised, and we 

 thus prevent further decomposition, and destroy the 

 power of the contagion, that is, its state of chemical 

 change. Muriatic and acetic acids, and in several 

 cases nitric acid, are to be preferred for this purpose 

 before all others. Chlorine also is a substance 

 which destroys ammonia and organic bodies with 

 much facility ; but it exerts such an injurious and 

 prejudicial influence upon the lungs, that it may be 

 classed amongst the most poisonous bodies known, 

 and should never be employed in places in which 

 men breathe. 



Carbonic acid and sulphuretted hydrogen, which 



