THEIR MODE OF ACTION. 37J 



The chemical action of such a compound is, of course, opposed 

 by the vital principle. The results produced depend upon the 

 strength of their respective actions ; either an equilibrium of both 

 powers is attained, a change being effected without the destruction 

 of the vital principle, in which case a medicinal effect is occa- 

 sioned ; 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 it 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. 



Another class of bodies 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 or- 

 gans. They produce a disturbance in the system, either by 

 their presence, or by themselves undergoing a change ; these are 

 medicaments. 



A third class of compounds are called foisons, when they pos- 

 sess the property of uniting with organs or with their component 

 parts, and when their power of effecting this is stronger than the 

 resistance offered by the vital principle. 



The quantity of a substance and its condition must obviously 

 completely change the mode of its chemical action. 



Increase of quantity is known to be equivalent to superior 

 affinity. Hence a medicament administered in excessive quan- 

 tity may act as a poison, and a poison in small doses as a 

 medicament. 



Food will act as a poison, that is, it will produce disease, when 

 it is able to exercise a chemical action by virtue of its quantity ; 

 or when either its condition or its presence retards, prevents, or 

 arrests the motion of any organ. 



A compound acts as a poison when all the parts of an organ 

 with which it is brought into contact enter into chemical combi- 

 nation with it, while it may operate as a medicine when it pro- 

 duces only a partial change. 



No other component part of the organism can be compared to 

 the blood, in respect of the feeble resistance which it offers to 

 exterior influences. The blood is not an organ which is formed, 



