PHYSIOLOGY. 79 



them ; and, as the sentient fibres of the nerves every where do 

 require, for their oscillation, to be kept in an extended state, for 

 which very purpose the arteries every where accompany them, 

 so the muscular fibres are every where in the same condition. 

 The blood-vessels in the bellies of muscles, and every where 

 accompanying them, are very numerous, as is allowed by all 

 anatomists ; and it appears evidently by injections, and micro- 

 scopical observations, that every single muscular fibre has its ar- 

 tery connected with it ; the principal trunks of the arteries in the 

 belly of a muscle, run parallel to the muscular fibres, and there 

 are every where such trunks interposed between them ; and these 

 parallel arterial vessels have every where a communication, but 

 they pass off at right angles. It was Dr. Hales who first point- 

 ed out this. Dr. Haller throws in several doubts with regard 

 to it ; but in the third edition of his Primes Linece, ( 398.) 

 which is since the publication of his other work, he seems to 

 have returned to the idea of Dr. Hales. In short, it appears 

 that there is a most industrious and plentiful distribution of 

 blood-vessels every where among muscular fibres, but that 

 they are arranged in a particular manner, which gives a 

 certain degree of tension to the muscular fibres in every part ; 

 and that such as are not stretched by the fluids distending the 

 arteries they surround, are yet no where left without some cause 

 of distention from this particular connexion with the arterial 

 system. By Sanctorius already it has been observed, ' quod 

 pondus addit roburj and we shall say that the tone or tension 

 of the muscular fibres is much the same with their vigour, 

 which will be easily understood from the proposition which 

 follows :" 



CIII. As the distention of muscular fibres, by LXXXIIL, 

 proves a stimulus (XC.), we conclude, that the tonic power in 

 them will, cceteris paribus, be in proportion to the degree of 

 tension (CII.) 



CIV. If the inherent power, as in XCVII. is in dependence 

 upon the nervous and animal powers and these may be increas- 

 ed or diminished by various means the tonic, as a part of the 

 inherent power, must, in some measure, be in proportion to the 

 state of the nervous and animal powers. " The language here 

 is, I hope, sufficiently clear; it expresses very much the same 



