26 Additional Notes. 



well as from the disobedience of the muscles and organs of sense to 

 their usual stimuli; but this less production of sensorial power must 

 depend on the inactivity of the glands, which compose the brain, and 

 are believed to separate it perpetually from the blood; and is thence 

 owing to a similar cause with the inaction of the fibres of the other parts 

 of the system. 



It is finally easy to understand how the fibres may cease to act by 

 the usual quantity of stimulus after having been previously exposed to 

 a greater quantity of stimulus, or to one too long continued; because 

 the expenditure of sensorial power has then been greater than its produc- 

 tion; but it is not easy to explain why the repetition of fibrous contrac- 

 tions, which during the meridian of life did not expend the sensorial 

 power faster than it was produced; or only in such a degree as 

 was daily restored by rest and sleep, should at length in the advance 

 of life expend too much of it; or otherwise, that less of it should be 

 produced in the brain; or reside in the nerves; lastly that the fibres 

 should become less excitable by the usual quantity of it. 



5. But these facts would seem to show, that all parts of the system 

 are not changed as we advance in life, as some have supposed; as in 

 that case it might have preserved for ever its excitability; and it 

 might then perhaps have been easier for nature to have continued her 

 animals and vegetables for ever in their mature state, than perpetually 

 by a complicate apparatus to have produced new ones, and suffer the 

 old ones to perish ; for a further account of stimulus and the conse- 

 quent animal exertion, see Zoonomia, Vol. I. Sect. 12, 



II. Means of preventing old age. 



The means of preventing the approach of age must therefore con- 

 sist in preventing the inexcitability of the fibres, or the diminution of 

 the production of sensorial power. 



1. As animal motion cannot be performed without the fluid matter 

 of heat, in which all things are immersed, and without a sufficient 

 quantity of moisture to prevent rigidity : nothing seems so well adapted 

 to both these purposes as the use of the warm bath ; and especially in 



