POISONS, CONTAGIONS, MIASMS. 329 



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 

 proportion in which the elements of a body are 

 united. Whatever form the first may assume, the 

 empirical expression must always remain un- 

 changed. 



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 

 action 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- 

 bination with their substance. The action of sul- 

 phuric, muriatic, and oxalic acids, hydrate of 

 potash, and all those substances which produce the 

 direct destruction of the organs with which they 

 come into contact, may be compared to a piece 

 of iron, which can cause death by inflicting an 

 injury on particular organs, either when heated to 

 redness, or when in the form of a sharp knife. 



