THEIR MODE OF ACTION. 



ail invariable product of the decomposition of animal matter. 

 The presence of ammonia in the air of chambers in which dis- 

 eased patients iie, 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 ammonia 

 does. The ammoniacal salts, also, 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 odor most closely 

 resembling that of corpses, or the peculiar smell of dunghills. 



By evaporating acids in air containing gaseous contagions, the 

 ammonia is neutralized, and we thus prevent further decomposi- 

 tion, 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 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 are fre- 

 quently evolved from the earth in cellars, mines, wells, sewers, 

 and other places, are amongst the most pernicious miasms. The 

 former may be removed from the air by alkalies ; the latter, by 

 burning sulphur (sulphurous acid), or by the evaporation of nitric 

 acid. 



The characters of many organic compounds are well worthy 

 of the attention and study both of physiologists and pathologists, 

 more especially in relation to the mode of action of medicines 

 and poisons. 



Several of such compounds are known, which to all appear- 

 ance are quite indifferent substances, and yet cannot be brought 

 into contact with one another in water without suffering a com- 

 plete transformation. All substances which thus suffer a mutual 

 decomposition, possess complex atoms ; they belong to the highest 

 order of chemical compounds. For example, amygdalin, a con- 

 stituent of bitter almonds, is a perfectly neutral body, of a slightly 

 bitter taste, and very easily soluble in water. But when it is 

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