PHYSIOLOGY. 115 



of the mind, or with regard to its manner of acting. I say" 

 But, at the same time, it is with little probability alleged, that 

 the administration of the corporeal functions is entirely directed 

 by the mind acting independently of the body, and with intelli- 

 gence perceiving the tendency of impressions, and exciting such 

 motions as may favour the beneficial, or obviate the hurtful 

 tendency, of all causes acting upon the body. " This is a short 

 account of the Stahlian system of which we have so often spoken. 

 When a poison is thrown into the stomach, the common lan- 

 guage of physicians is that poison has the power of stimulating 

 the stomach, and is thereby thrown out, and the further injury 

 prevented. The language of the Stahlians is this that poison 

 has no peculiar power of exciting vomiting ; but the soul, as 

 soon as it perceives its being present, knowing the consequences', 

 excites the stomach to throw it out. Now this is the mind act- 

 ing independent of the powers of impression, and of the modi- 

 fications of sensations, which, the Stahlians say, give only in- 

 telligence. These sensations, they maintain, do not necessarily 

 excite the brain to the volition of an action in consequence : 

 but the soul, perceiving the baneful or hurtful tendency, favours 

 or resists the operation, and occasions all that follows after." 



We are certainly conscious of no such administration. Many 

 impressions have their effects without sensation or volition. In 

 most cases where volition takes place, it is very general, with 

 little consciousness of the motions excited, and none at all of the 

 organs employed. The force of impression is every where ab- 

 solute ; and it is according to the force of impression, and other 

 mechanical conditions of the system, that the motions excited 

 prove either salutary or pernicious. The general principle, 

 therefore, is ill founded; it is not necessary (Vide Stahl, 

 Praef. ad Juncker. Consp. Med.) ; it can be of no use, and 

 may be hurtful to the system of physic. 



CXXIII. The action of the brain is often determined and 

 regulated by custom and habit ; that is, by laws established by 

 frequent and uniform repetition. See above (XLIII. LIV. 

 LV. LVI. 5. LX. 3. LXVIII. and LXX.) for the effects of 

 custom on sensation, and CXIV. for one effect of it on the 

 action of moving fibres. It is now to be observed, further, 1. 

 That custom determines the degree of tension (CII. CIII.) ne- 



