72 Borelli and the Influence [lect. 



fibres and muscular fasciculi as the real contractile part, the 

 fibres of the tendon serving only to bind the fleshy fibres to 

 bones or other structures. It is true that he refutes Stensen's 

 mathematical mechanical conceptions of the arrangement of 

 the fibres, replacing them by conceptions of his own ; but this 

 is a matter of little moment. Both observers had grasped the 

 all important fundamental fact that the act of contraction is 

 carried out by the fleshy muscular fibre and that the fibres of 

 the tendon, howsoever far they may seem to enter the muscle, 

 are mere passive agents, retaining their normal length and 

 consistence and taking no part whatever in the contraction. 

 The old idea of the contractile tendinous fibres, and of the flesh 

 'caro,' serving the purpose of mere packing was done away 

 for ever, and Vesalius was justified of his children. 



Coming then to the actual nature of this contraction of 

 the fleshy part, Borelli strove very hard to reach a definite 

 mechanical explanation of the process. In this he, in one 

 respect, went distinctly astray. Recognizing the beat of the 

 heart as a contraction of the muscular ventricles, and im- 

 pressed with the fact that, during the systole the walls of 

 the ventricles closing in laterally obliterate the cavities from 

 which the blood has been driven, he concluded that the 

 muscular walls in contracting increase in bulk ; and he ex- 

 tended this conclusion to all muscles. This view of an 

 increase in bulk led him to suppose that the hardening and 

 tension observable when a muscle contracts is due, not to 

 mere displacement of the parts of the muscle itself, but to 

 an inflation of the muscular substance by something from 

 without. And in accordance with this he constructs a hypo- 

 thesis, in which the muscular fibres are supposed to be chains 

 of rhombs, and proceeds to shew how contraction, with its 

 attendant hardening and extension, may be explained by 

 considering inflation as being the sudden insertion of a number 

 of wedges. 



Having reached this mechanical conception of the act of 

 contraction itself, he attempts to gain a like mechanical 

 conception of the way in which the nerves act as the exciting 

 agents of this contraction. He begins his discussion of the 



