Old Age and Death. 3 1 



is, in common language, the acquired habit assists the power of the 

 stimulus; see Zoonomia, Vol. I. Sect. XXII. 2. and Sect. XII. 3. 3. 



On this circumstance depends the easy motions of the fingers in 

 performing music, and of the feet and arms in dancing and fencing, 

 and of the hands in the use of tools in mechanic arts, as well as all 

 the vital motions which animate and nourish organic bodies. 



On the contrary, many animal motions by perpetual repetition are 

 performed with less energy; as those who live near a waterfall, or a 

 smith's forge, after a time, cease to hear them. And in those infec- 

 tious diseases which are attended with fever, as the small-pox and 

 measles, violent motions of the system are excited, which at length 

 cease, and cannot again be produced by application of the same 

 stimulating material; as when those are inoculated for the small-pox, 

 who have before vmdergone that malady. Hence the repetition, 

 which occasions animal actions for a time to be performed with 

 greater energy, occasions them at length to become feeble, or to 

 cease entirely. 



To explain this difficult problem we must more minutely consider 

 the catenations of animal motions, as described in Zoonomia, Vol. I. 

 Sect. XVII. The vital motions, as suppose of the heart and arterial 

 system, commence from the irritation occasioned by the stimulus of 

 the blood, and then have this irritation assisted by the power of asso- 

 ciation ; at the same time an agreeable sensation is produced by the 

 due actions of the fibres, as in the secretions of the glands, Avhich 

 constitutes the pleasure of existence; this agreeable sensation is inter- 

 mixed between every link of this diurnal chain of actions, and contri- 

 butes to produce it by what is termed animal causation. But there is 

 also a degree of the power of volition excited in consequence of this 

 vital pleasure, which is also intermixed between the links of the 

 chain of fibrous actions; and thus also contributes to its uniform easy 

 and perpetual production. 



The effects of surprise and novelty must now be considered by the 

 patient reader, as they affect the catenations of action; and, I hope, 

 the curiosity of the subject will excuse the prolixity of this account 

 of it. When any violent stimulus breaks the passing current or cate- 

 nation of our ideas, surprise is produced, Avhich is accompanied with 



