On the Nemjous Power, and il$ Mode ofaiiing, 893 



anfe from an examination of the circumftances of their fail- 

 ing, icem to me to be of great importance, and difficult to be 

 removed. 



I am therefore far from aflerting that ihefe ftones which 

 have fallen \o the earth are to be confidered as mafl'es pro- 

 jec^^ed from die moon ; nor does Laplace make anv fuch af- 

 fertion. Hisobje<ft, as well as mine, is to (how philofophers 

 engaged in refearches on this fubje^t the poffibility of thefe 

 malfes having a felemtic origin. It is much to be wiftied 

 that the ingenious Chladni would favour us with a new edi- 

 tion of his celebrated eflay on the mafs of iron found ip Si- 

 beria *, as he no doubt would be able, from Benzenbergand 

 Brandes' Obfervations on falling Stars, Howard's Chemical 

 Kxamination, and from various other documents, to make 

 confidtrable additions to it. 



I 



LIT I. On the Nervous Po^ver, and its Mode ofa^ingf. 



T -has been generally fuppofed by phyfiologifts that the 

 power by which fenfations were tranlmitted to the fenforium, 

 was likewife the medium by which mental impreflions were 

 communicated to the body. But this opinion is totally in- 

 confiltent with that moli frequent obfervation, that very often 

 every poifible fufceptibility of fcnfaiion is lo(l in a whole 

 limb, which neverthc'efs retains voluntary motion. This 

 appears inoft ftrikingly in the St. Viius's dance, which de- 

 prives the affliclcd parts of every fufceptibility of fenfation 

 without deftroying voluntary motion. And, oa the contrary, 

 there are cafes where the fun«5linns of the fenles remain un- 

 impaired, and are fomeiiines incrcafed, while the mufcular 

 motion is completely loft. In order to explain this phaeno- 

 menon two kinds of nerves have been hypotheiicully adopted, 

 nerves of fenfation and nerves of motion; but without ren- 

 dering the explanation more fatisfa^lory. Certain it is, that 

 the action of mental irritation upon the bodv, and the com- 

 munication of the fenfations witli the fenforium, are effects 

 of two different powers, which cannot poffibly have their 

 feats in one and the fame organ. 



That which is underflood by the word nerves confifls pro- 

 perly of two entirely dilferent parts, the medullary fubjlance 



* \l'>tx lien orlprunjj Jcr von Pnllas u;cfundcntw und andcrcr ihr nlin- 

 fichiT KiCt'n m<n'cn, uiitl libit tipig'e diiiTiii in verbinclnnij b ebctju Na- 

 mr-eifchcinuni^'n J VcrHC. '1". T. CMaclni. Rigai^g.j. 410. 



f Fioni Kill's JubJv JU> dk Pbvfologi^;, vol. i. 



03- of 



