POISONS, CONTAGIONS, MIASMS. 373 



of mineral coal. Hydrogen, on the contrary, is dis- 

 engaged from the constituents of mineral coal in the 

 form of a compound of carbo-hydrogen ; a complete 

 removal of all the hydrogen would convert coal into 

 anthracite. 



The formula C36 H22 022, which is given for 

 wood, has been chosen as the empirical expression 

 of the analysis, for the purpose of bringing all the 

 transformations, which woody fibre is capable of 

 undergoing, under one common point of view. 



Now, although the correctness of this formula 

 must be doubted, until we know with certainty the 

 true constitution of woody fibre, this cannot have 

 the smallest influence on the account given of the 

 changes to which woody fibre must necessarily be 

 subjected in order to be converted into wood or 

 mineral coal. The theoretical expression refers to 

 the quantity, the empirical merely to the relative pro- 

 portion in which the elements of a body are united. 

 Whatever form the first may assume, the empirical 

 expression must always remain unchanged. 



CHAPTER Xni. 



ON POISONS, CONTAGIONS, AND MIASMS. 



A GREAT many chemical compounds, some derived" 

 from inorganic nature, and others formed in animals 

 and plants, produce peculiar changes or diseases in 

 the living animal organism. They destroy the vital 

 functions of individual organs; and when their ac- 

 tion attains a certain degree of intensity, death is 

 the consequence. 



The action of inorganic compounds, such as acids, 

 alkalies, metallic oxides, and salts, can in most cases 

 be easily explained. They either destroy the con- 

 tinuity of particular organs, or they enter into com- 



32 



