



VOL. LXXVIII.]] PHILOSOPHICAL TRANSACTIONS. 303 



power with which it was pricked by the needle; this contraction was therefore 

 not communicated to it by the moving needle, but was generated, and therefore 

 an original motion. 



In all communicated motion, by which two bodies at a distance are brought 

 near to one another, there must subsist some other matter, by which they may 

 be drawn, or forced, nearer to one another; but in original motion, it is not at 

 all necessary that any other matter should exist at all. Two particles, placed at 

 as great a distance from one another as the sun is from the earth, as before ob- 

 served, though at perfect rest, would begin to move nearer one another, by the 

 attraction of gravitation, if all other matter whatever were annihilated. 



Most authors who have treated on muscular motion have supposed that it was 

 a communicated motion; and that it was produced by something passing by the 

 nerves, from the brain to the moving part. Three doctrines have been set forth; 

 one, that there is a fluid passing along the nerves ; a 2d, that there is a vibration ; 

 and a 3d, that the nerves are surrounded with something like electric matter, in 

 which motion runs from the brain to the moving parts. Those who have consi- 

 dered this subject must be tired of the arguments which have been brought to 

 refute each of these; for no argument from fact has been employed to prove any 

 one of them : I shall therefore leave them as mere chimeras of the brain. I have 

 taken notice, that it is not requisite for any motion to pass between two bodies, 

 exciting in each other an original motion, through or by any other matter: I 

 have also shown, that muscular motion is an original motion: it follows, that it 

 is not necessary for any motion, or communication, to pass through any other 

 matter, in order to bring the muscular fibres into action. 



One case of muscular motion is, when a stimulus is applied to some part of 

 the body, and a muscle at a distance immediately contracts. It has been sup- 

 posed in this case, that some influence was communicated to the nerve of the 

 part where the stimulus was applied, and through it to the brain, and from the 

 brain through the nerves of the contracting muscle. Granting, for a little, that 

 some motion may pass along the nerves, and therefore that the end of the nerve, 

 where the application was made, may be the part in which the original motion 

 began, the stimulus frequently does not touch the end of the nerve; for if 

 vapour of volatile alkali be applied to the nostrils, a universal glow of heat, and 

 increased circulation, will constantly take place; but the vapour of the volatile 

 alkali could not touch the nerves of the nostrils, the membrane being constantly 

 covered with mucus, which the vapour could not penetrate without dissolving it, 

 which it had not time to do, and, if it had, would have united with it, so as to 

 form a soap, void of any stimulating power. 



If therefore the original motion began in the end of the nerves of the nostril, 

 it must be excited by a substance at a distance from the end of that nerve, with- 



3a2 



