70 LECTURE 11. 



taining a saturated solution of salt, and 

 throw into it a single crystal ; the act of 

 crystallization would begin from the point 

 touched, and rapidly and regularly pervade 

 the liquor till it assumed a solid form. Yet 

 I know I should incur your ridicule, if I 

 suggested the idea that the stimulus of the 

 salt had primarily excited the action, or 

 that its extension was the effect of conti- 

 nuous sympathy. If also I threw a spark 

 amongst gun-powder, what would you 

 think were I to represent the explosion as 

 a struggle resentful of injury, or the noise 

 as the clamorous expression of pain ? 



Now though chemists may solve the 

 cause of these phaenomena, physiologists 

 have yet to learn, and probably they 

 never may learn, why certain actions 

 succeed to certain causes in living bodies. 

 Causes which induce muscular or nervous 

 actions in one part, do not induce similar 

 actions in another. Both muscles and nerves 

 have peculiar habitudes and modes of ac- 

 tion, and require the application of various 

 peculiar excitements. Causes which pro- 



