THEIR MODE OF ACTION. 395 



When a chemical compound of simple constitution 

 is introduced into the stomach, or any other part of 

 the organism, it must exercise a chemical action 

 upon all substances with which it comes in contact ; 

 for we know the peculiar character of such a body 

 to be an aptitude and power to enter into combina- 

 tions and effect decompositions. 



The chemical action of such a compound is of 

 course opposed by the vital principle. The results 

 produced depend upon the strength of their respec- 

 tive actions ; either an equilibrium of both powers is 

 attained, a change being effected without the de- 

 struction of the vital principle, in which case a medi- 

 cinal effect is occasioned; or the acting body yields 

 to the superior force of vitality, that is, it is digested ; 

 or lastly, the chemical action obtains the ascendency 

 and acts as a poison. 



Every substance may be considered as nutriment, 

 which loses its former properties when acted on by 

 the vital principle, and does not exercise a chemical 

 action upon the living organ. 



Bodies of another class change the direction, the 

 strength, and intensity of the resisting force (the 

 vital principle), and thus exert a modifying influence 

 upon the functions of its organs. They produce a 

 disturbance in the system, either by their presence, 

 or by themselves undergoing a change ; these are 

 medicaments. 



Compounds of a third class are called poisons, 

 when they possess the property of uniting with or- 

 gans or with their component parts, and when their 

 power of effecting this is stronger than the resis- 

 tance offered by the vital principle. 



The quantity of a substance and its condition must 

 obviously completely change the mode of its chemi- 

 cal action. 



Increase of quantity is known to be equivalent to 

 superior affinity. Hence a medicament administered 

 in excessive quantity may act as a poison, and a 

 poison in small doses as a medicament. 



