170 CERTAIN REMEDIES TAKE A 



We are acquainted with a multitude of sub- 

 stances, which exercise a most marked influence on 

 the act of transformation as well as on the nutritive 

 process, while their elements take no share in the 

 resulting changes. These are uniformly substances 

 the particles of which are in a certain state of 

 motion or decomposition, which state is communi- 

 cated to all such parts of the organism as are ca- 

 pable of undergoing a similar transformation. 



75. Medicinal and jDoisonous substances form 

 a second and most extensiye class of compounds, 

 the elements of which are capable of taking a direct 

 or an indirect share in the processes of secretion 

 and of transformation. These may be subdivided 

 into three great orders ; the first (which includes 

 the metallic poisons) consists of substances Vvdiich 

 enter into chemical combination with certain parts 

 or constituents of the body, Avhile the vital force 

 is insufficient to destroy the compounds thus formed. 

 The second division, consisting of the essential oils, 

 camphor, empyreumatic substances, and antiseptics, 

 &c., possesses the property of impeding or retarding 

 those kinds of transformation to which certain very 

 complex organic molecules are liable ; transforma- 

 tions which, when they take place out of the body, 

 are usually designated by the names of fermentation 

 and putrefaction. 



The third division of medicinal substances is 

 composed of bodies, the elements of which take a 

 direct share in the changes going on in the animal 



