BRA 



BRA 



vremayliave no fenfation from the mod violent impulfes, for 

 fncli \ve cannot but fuppofe to take place wtien a limb is re- 

 moved by a cannon ball, n circumftance \vhicl\ I'as happened 

 witliout the confcioufncis of the perfou to whom it has 

 j occurred. 



! Thefe hypothefes appear to us adequate to explain all the 

 circuniftanceslhat have bei-n noticed relative to the fuiidtions 

 1,1 the neivo\is Ivileni. To review the circumilanccs, even 

 with the greatelt poffiblc brevity, would render this article 

 to ) extenlive. Yet, there are ionie particulars which the 

 leader may expe^it that we fliould advert to. Of tlieie, it 

 is right to mention, that the dilpofuioii of the nerves to ait, 

 is increafed, as the canfes exciting their aftion is diniinidicd. 

 This circumllance has been exprtfTcd, we can fcareelv fay 

 explained, by the late Doftor Brown, in his " Elementa 

 r.Iedicinx," by faying-, that the excitability of the nerves is 

 :!cciimnlated in proportion to the deficiency of the cxcitiif^ 

 Liuifes. 1'his fatt is prodnf^ive of conieipiences which ap- 

 [lear particulaily beautiful and ufeful ; it luruilhes H power 

 tit accommodation in our fenfts to the varying circumllances 

 ol life. Thus, for inltance, a perfon confined in the dark, 

 fliall receive the iniprcfiion of fight from a very fniall quan- 

 tity of light, and his eyes would even be injured by t!ie com- 

 mon day-light. Tlie reverfe of this is equally true : that a 

 '.icrfon Ihall live in a llrong light, till his eyes become fo 

 ;.ecuttomed to it, that a lefs quantity Ihall not produce a 

 proper impreffioii ; or a perfon, wlio has long been in a Hill 

 and iilent place, ihall hear the flightell found, fuch as would 

 he imperceptible to one whole auditory nerves had, lor fome 

 time, been accuiionied to the forcible imprellioiis of the air, 

 made by loudly founding' bod,, s. This power of accom- 

 modation does not only belong to particular feiifes, but 

 it will bear a more univtrfal application. A perfon, living a 

 iUXurioMS hie, v.-ho avoids every fenfation which gives him 

 vhe leall uneafinels, and who attends only to the gratifica- 

 lion of his plenfnrcs, renders his nervous fyftem too fenfible : 

 he flirinks at the cold wind, he is llartled at a lond 

 noife ; and every rough impreffion, which would not dif- 

 quiet another, owing to his ill-judged indulgence, dillrefTcs 

 him. Let us remark the contraft in a hardy feanian, who 

 lias indured the inclemency of the weather, who has fuftained 

 fatigue and pain: if the winds blow, or the cannon thun- 

 der, he hears the one, and feels the other, but they do not 

 much affect him ; and from being habituated to ieiifations, 

 at lirit painful, he is afterwards nna.fctted, even by thofe im- 

 jncirioi'.s which would hurt a man living in the n.edium be- 

 tween thefe two extremes. 



It feems alfo right here to remark, that a great finiilarity 

 appears to exif* between the fuppofed irritable attions of 

 the nerves, and thofe of the mufcles. The facility, accu- 

 racy, and celerity of the actions of nerves are improved 

 by ufe, as is exemplified in the correft and quick feniations 

 of thofe perfons v/ho are accuftomcd to exercife their audi- 

 tory nerves in attending to mufical founds. 



A train or fiiecelTion of nervous aftions having taken place, 

 they become concatenated, and are liable to recur in fuccef- 

 fion, if one of thefe aiiions is accidentally induced. 



Both the nerves and mufcles feein to require temporary 

 refpites fromaftioa, and both appear to be refrclhed by flcep. 



The fuppofition of aflions occurring in the nerves, explains 

 many circumftances connefted with difeafes. Vehement 

 aftions may be begun independent of impulfes in the tangible 

 ♦■xtremities of nerves, and thus occallon fevere pains. This 

 feems to happen in the difcafe called tic doloureux. Ordi- 

 narily, actions begun in the tangible extremities of the nerves, 

 are regularly tranfmitted to the brain ; but in cafes of nervous 

 pains, the aition feems to begin iii the middle of the nerves. 



Vol. V. 



It is alto probable, that aftions may take place in the fenforial 

 extremities of the nerves producing illufory fenfations, and 

 thus exciting ideas. 



The next fubjtdt which claims our attention, is the part of 

 the brjin to which all the nervous motions, produced by ex- 

 ternal imjueflions, lend, and from which al! the motions 

 nriling from volition begin. Phyfiologiils have agreed to 

 call this part the fcnforinm, and have fuppofed it to he 

 fituated in various parts of the brain ; but there is no part 

 of the brain to which this importance lias been afcribed, 

 which has not been oecafiunally found difeafcd, without fen- 

 fation and volition being impeded. Of late, SoemmtTinff 

 has iifRrmed, that he can trace all the nerves to the ventricles 

 of the brain, in which he thacfore fuppofes the faculty of 

 fenfation and volition to refide. All our feiifes may be gra- 

 tified at the fame time, and we may give a preference to the 

 'pleafure which we receive from one of them, above that 

 which we derive from the others ; which circumllance feems 

 to prove the unity of that wliich perceives and determines. 

 Ualler, after confidering the fubjett, thus concludes : " Nunc 

 quidem in nniverfum obfervamus, non debere angufliorem aiii- 

 ni3E fcdem poiii, quani lit conjunfla omnium nervorum origo ; 

 neqne particulam aliquam pro ea fede offerri, nifi ad quam 

 omnes nen'os ducere poflimus. Facile enim intelligitur, 

 debere a fenforio commnni nullum uUin.s particuLc corporis 

 animati fenfum abelfe," &-c. Elem. I'iiyfio!. 



If it be admitted that fenfation and volition exift in the 

 brain, it mull alio be granted that motions m\ift be produced 

 in the fenforial extremities of the nerves by the objetts of 

 fenfe, and that refleited motions mufl take place in the 

 nerves, by which the mandates of the will are tranfmitted to 

 the mufcles. 



If all that has been faid were to be afcertained, the extent 

 of our knoivledge would, in that cafe, only lead to this con- 

 clurioii, that motions of a fubtile fubllancc took place in the 

 feiifbrinm, and from fuch motions we elleem it impoflible to 

 account for fenfation. We can conceive no varieties in thefe 

 motions but thofe which relate to degree or duration. We 

 feel It impoflible to believe that fenfation can be the refiilt of 

 fuch motions, or that ideas can arife from any fucceflion or 

 train of them. We therefore conclude, with many celebrated 

 phyliologifts, and men of the founded underflanding and 

 greatefl refleftion, in the natural belief, that fenfation, remem- 

 brance, companion, judgment and volition are properties of 

 a dilliud fubllance. 



The conclulion to be drawn from this examination of the 

 funftions of the brain and nerves, and from that of the other 

 animal functions, feems curious and intcrclling. We perceive 

 an exafl correfpondence in the opinions we obtain from 

 phyfiological refearches, and thofe which arife fo naturally 

 from the fuggellions of reafon, that they have been confi- 

 dercd as intuitive. For moft reflecting perfons in all ages of 

 the world have believed, and it is, indeed, natural to believe, 

 what modern phvliology teaches, that in the human body 

 there exifls an afTernblage of organs, formtd of common inert 

 matter, fuch as we fee in the dead l^ate, a principle of life 

 and motion, and a ftntient and rational faculty, all intimately 

 connefted, yet each diftiiidt from the other. 



Braik, Chcnucd} Aiialyfis of. Though the analyp.s of this 

 moft important organ can throw no light on its peculiar 

 funflions, it is in itfelf fufficiently remarkable to Le detailed 

 fomewhat at length. 



It is needlefs to give all the conjectures on the nature of 

 brain, made before clKmilts had acquired a tolerably accurate 

 and juft method of analyzing animal matter. The experi- 

 ments of real importance are chiefly thofe of 1 nourtt, ia 

 ijco, with i'orae lubfequent additions by Fourcroy. 



D d The 



