24 GENERAL VIEW OF THE FUNCTIONS. 



in the mind, as in seeing, hearing, tasting, smelling, feeling: 

 animal contractility is excited by the volition of the mind con- 

 veyed to the voluntary muscles by means of the nerves. Organic 

 sensibility is attended by no perception, and is followed by con- 



together ; blisters relieve internal inflammation, and irritate the more difficultly 

 in proportion to the violence of the internal disease. The same phaenomena are 

 observable in animal sensibility and in the mind at large : 



" Tut, man ! one fire puts out another's burning, 



One pain is lessen'd by another's anguish ; 

 Turn giddy, and be holp by backward turning ; 



One desperate grief cures with another's languish ; 

 Take thou some new infection to thy eye, 

 And the rank poison of the old will die." 



SHAKSPEARE. Romeo and Juliet, act i. sc. ii. 



The effect of vicissitudes of temperature, and a large number of other patho- 

 logical phaenomena, are principally explicable on the derangement of the balance 

 of excitability, and for the most part, consequently, of circulation. 



Notwithstanding it is a general law that the effects of an agent diminish 

 the more frequently it is applied, and vice versa, as shown on the one hand, in 

 the large quantities of spirituous liquors which persons at length bear, and on 

 the other by the violent inflammation excited by the application of warmth to 

 parts exposed to intense cold ; yet, if a stimulus is applied so energetically as to 

 leave the sensibility heightened, especially if to the point of inflammation, its 

 subsequent power is greatly increased. Immense potations of spirituous liquors 

 may gradually be borne, but if the increase is too great, the sensibility of the 

 stomach may become such that a single glass will prove violently irritating. 



The general law, to which the effects of agents, in proportion to their previous 

 application, is referable, appears to be this ; that an agent acts according 

 to the difference between its strength and the strength of the former application. 

 Thus, if the right hand be immersed in water of 30, and the left in water of 50, 

 and both are removed to water of 70, the effect of the water at 70 upon the 

 right hand will be greater than upon the left, on account of the difference between 

 30 and 70 being greater than between 50 and 70; and this explains the 

 glow of the cold bath, as, during immersion, there is less stimulus, and, on emerg- 

 ing, the temperature of the atmosphere, and the re-admitted blood into the super- 

 ficial vessels, though stimuli absolutely of the same strength as before immersion, 

 are, comparatively, more powerful than what the system experienced during 

 immersion. 



The specific action of one agent frequently prevents or destroys that of another : 

 v. c. small-pox and measles very rarely occur together ; the former disease is 

 frequently prevented for ever by the cow-pock ; bark cures the effect of marsh 



