On Muscular Motion and Animal Spirits 291 



it. Indeed, if the finger be held at some distance from 

 the left ventricle, when the heart contracts the side 

 of that ventricle will be briskly dashed against the 

 finger. And that this is really the case has already 

 been remarked by the eminent men, our own 

 Harvey and Lower. 



Harvey held that this kind of pulsation of the 

 heart arises thus : that while the walls of the 

 ventricles contract as to length, they must increase in 

 thickness, just as when other muscles contract they 

 swell up, becoming broader. T admit that the walls of 

 the ventricles of the heart do in contraction become 

 somewhat thicker, but it is scarcely credible that they 

 swell up sufficiently to account for the pulsation 

 against the chest ; for it has been made out that 

 muscles do not in their contraction swell up so much 

 as is commonly believed. 



I think, then, that we should hold as to the pulsation 

 of the heart, that the fibres of the heart, in their 

 contraction, draw its cone towards its base as to the 

 more fixed end ; whence it comes about that the 

 walls of the ventricles are carried outwards, the 

 pressure of the contained blood contributing to this. 

 To this it may at once be objected, with Harvey, 

 that a curved fibre in contracting becomes straighter 

 and is not distended in a circle, and so as the walls 

 of the ventricles of the heart are in a circular position 

 they will be carried inwards towards a straight line, 

 and not outwards. I reply, if both ends of the curved 

 fibre were fixed, it would, when shortened, be brought 

 towards a straight position ; but if one of the ends of 

 the fibre be movable, and even is in fact moved, 

 it can, in its contraction, be distended circularly : for, 

 in Plate III., Fig. 9, let ^, i, b, be a curved fibre, or the 

 internal wall of the left ventricle of the heart, and a^ e^ 



