On Mtiscidar Motion and Animal Spirits 237 



they should contract and swell up so much, inas- 

 much as their series are, as is shown in the figure 

 referred to, arranged according to the length of the 

 muscle, so that the contraction of the muscle will be 

 equal to that of the fibrils. But now, as nature is in 

 the habit of taking the shortest road, it is probable 

 that the contraction of the muscle is produced by the 

 contraction of the fibrils rather than by that of the 

 fibres. And it also tells in favour of this, that, as the 

 fibrils are very small and very short, their contraction 

 even to a half would scarcely be anything remarkable ; 

 for as the fibrils suffer contraction as a whole, the case 

 is just as if fibres stretched according to the length of 

 the muscle were forced into manifold corrugations, 

 and their contraction, taking place thus, although it 

 be pretty great, can yet occur without notable swell- 

 ing of the muscle. 



To these T further add that the shortened fibrils 

 draw the fleshy fibres together and constrict them : so 

 that it is probable that the contraction of the muscles 

 is accomplished by the fibrils ; inasmuch as a muscle 

 when contracted is conspicuously constricted and 

 becomes hard ; and it does not seem that this could 

 take place in any other way than by the contraction 

 of the fibrils. But there will be a fuller discussion of 

 the constriction of the contracted muscle later. 



Moreover, it is nature's custom very often to carry 

 on her operations by means of very small things, so 

 that the fibres seem too thick and coarse for muscular 

 contraction to take place primarily in them ; and it is 

 probable that they serve rather for transmitting blood 

 than for carrying on animal motion, as will be shown 

 below. 



Lastly, it tells in favour of this, that the shortness 

 of the fibrils and their almost infinite number con- 



