84 LETTERS TO BROTHER JOHN. 



You will now readily understand of what tremen- 

 dous importance to health are the properties con- 

 tractility and sensibility : for, as health consists in 

 the due performance of certain actions, and as these 

 actions depend on contractility and sensibility, it is 

 clear that they will be feebly or energetically per- 

 formed, accordingly as these two properties are 

 themselves energetic or feeble. You will also 

 see, that the stimulus which the blood offers to 

 them is of vast importance likewise. This stimulus 

 is a sort of messenger, sent to summon them to 

 action. In proportion as the summons is feebly 

 delivered, it will be faintly heard, and feebly obeyed. 

 Contractility and sensibility are like a horse that gal- 

 lops furiously, moves sluggishly, or goes to sleep 

 entirely, exactly in proportion as the stimulus of the 

 whip is gently or vigorously applied. Like the horse, 

 too, the faster they are urged forward by the whip, 

 the sooner they become tired ; like him, they may 

 be driven even to death; like him, they require rest 

 and repose. Do not therefore be led to undervalue 

 the importance of these properties, because of the 

 playfulness with which 1 have occasionally spoken 

 of them ; as, for instance, in the allusions to Paga- 

 nini 'and his fiddle. " Ridentem dicere verum 

 quid vetat?" What reason on earth is there for 



