On Muscular Motion and Animal Spirits 231 



given, spring forth from the tendinous into the fleshy 

 fibres, and there, meeting active particles of another 

 sort, supplied by the blood, immediately effervesce with 

 them, so that from the struggle and agitation of them 

 both, the fleshy fibres, being lax and porous, are stuffed 

 out and corrugated, and that the contraction of the 

 muscle is produced by the corrugation at the same 

 time at both ends of all these fibres. But when the 

 contraction is over, the unused spirits that are left 

 again in great part retire into the tendinous fibres, 

 leaving the other particles within the fleshy fibres, 

 and then the blood, as also their nerves repair the 

 waste of these fibres. But as to how the spirits stored 

 in the tendinous fibres are brought thence into the 

 fleshy fibres for the production of motion," our learned 

 author supposes " that an impulse transmitted by the 

 nerves, as it were a token, is required, and that this 

 is done by other spirits sent from the brain, while, 

 namely, these inflowing spirits, by their varying 

 approach to the muscles, regulate the innate spirits in 

 their various movements, whether of expansions or of 

 retreats." 



This theory of the learned author is certainly very 

 ingenious, but I am not sure that it is in the same 

 degree in accordance with truth. 



For, in the first place, the inflation of the fibres in 

 the way described is beset with various difficulties, 

 and these of no small weight. For if a muscle is con- 

 tracted by the inflation of its fibres, it would neces- 

 sarily follow that, being distended towards the outside 

 in its contraction, it would swell into a much greater 

 size ; but it has been found by observation that a 

 contracted muscle is drawn more closely together and 

 becomes hard, and that, if it does not become smaller, 

 yet certainly it does not swell up to such an extent as 



