408 POISONS, CONTAGIONS, MIASBIS. 



or, to describe the change more correctly, the state 

 of decomposition of the dissolved contagious matter 

 is completed in the water. 



All gases emitted from putrefying animal and 

 vegetable substances in processes of disease, gener- 

 ally possess a peculiar nauseous offensive smell, a 

 circumstance which, in most cases, proves the pres- 

 ence of a body in a state of decomposition. Smell 

 itself may in many cases be considered as a reaction 

 of the nerves of smell, or as a resistance offered by 

 the vital powers to chemical action. 



Many metals emit a peculiar odor when rubbed, 

 but this is the case with none of the precious metals, 

 — those which suffer no change when exposed to air 

 and moisture. Arsenic, phosphorus, musk, the oils 

 of linseed, lemons, turpentine, rue, and peppermint, 

 possess an odor only when they are in the act of 

 eremacausis (oxidation at common temperatures). 



The odor of gaseous contagious matters is owing 

 to the same cause; but it is also generally accom- 

 panied by ammonia, which may be considered in 

 many cases as the means through which the con- 

 tagious matter receives a gaseous form, just as it is 

 the means of causing the smell of innumerable sub- 

 stances of little volatility, and of many which have 

 no odor. (Robiquet.)* 



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 de- 

 scribed, produces a white precipitate in a solution 

 of corrosive sublimate, just as a solution of ammonia 

 does. The ammoniacal salts also, which are obtained 

 by the evaporation of rain water after an acid has 



* Ann. de Chim. et de Phys. XV. 27. 



