Si THEPHILOSOPHY 



The braia and fpinal marrow are fuppofed to be the origin 'of all 

 the nerves or inftruments of fenfation. The nerves are, in general, 

 cineritious, fhining, inelaftic cords. But they differ from each other 

 in fize, colour, and confiftence. From numberlefs experiments and 

 obfervations, it is unqueftionable, that the nerves are the inftru- 

 ments both of fenfation and of animal motion. But, how thefe 

 effedts are produced by the nervous influence is a difcovery ftill to 

 be made. The inquiry, however, has given rife to feveral ingeni- 

 ous conjedures and hypothefes. Some phyfiologifts have maintain- 

 ed, that the nerves are folid cords, which may be divided into an 

 infinite number of minute filaments ; and that, by the vibrations of 

 thefe cords, the various impreffions and modifications of feeling are 

 conveyed to the brain. Others, with more plaufibility, have fup- 

 pofed, that the nerves are afferablages of fmall tubes ; that a fub- 

 tile fluid, fometimes called animal fpirits^ is fecreted in the brain and 

 fpinal marrow ; and that by the influence or motions of this fluid 

 all the fenfations of animals are tranfmitted to the fenforium, or ge- 

 neral repofitory of ideas. But it is needlefs to dwell upon a fubjedt 

 covered with darknefs, and which all the efforts of human powers 

 will probably never bring to light. 



Anatomifts have defcrlbed forty pair of nerves. Ten of them 

 proceed from the medulla oblongata of the brain, and thirty from 

 the fpinal marrow. Thefe nerves, by fending off innumerable ra- 

 mifications, are diftributed, like a net- work, over every part of the 

 body, till they terminate, in the form of minute papillae, upon the 

 {kin. That the nerves are the immediate inftruments of fenfation, 

 as well as of mufcular motion, has been proved by a thoufand un- 

 controvertible experiments. When the trunk of the fciatic nerve 

 is cut, the thigh and leg on that fide inftantly lofe all motion, and 

 all fenfe of pain, below the incifion, and neither time nor art can 

 ever reftore the power of feeling or of moving. But the parts be- 

 tween 



