2^0 DURATION OF MUSCULAR ACTION. 



ing the health under various circumstances, in preference 

 to every species of actual exertion. 



Part I. On the Duration of Muscular Action. 



Duration of 



Toiui'.uuy 



The necessity of occasional intermissions from a series of 

 laborious exertions is within the experience of every one; 

 the fatigue of continuing the effort of any one voluntary 

 muscle without intermiffion even for a few minutes is also 

 sufficiently knovfn ; but there i5 a third view of the dura- 

 tion of muscular action, which appears to have escaped 

 Every- action a the notice of physiologists ; for I believe it has not hitherto 

 peaw»l*effor'ts» ^*^^" observed, that each effort, apparently single, consists 

 in reality of a great number of contractions repeated at 

 extremely short intervals : so short indeed, that the inter- 

 mediate relaxation cannot be visible, unless prolonged be- 

 yond the usual limits by a state of partial or general 

 debility. 



Proof of this J j^j^yg been led to infer the existence of these alternate 

 noni the vibra- 



rorvsoundofa motions ffom a sensation perceptible upon inserting the ex- 

 iifigei mthe tremity af the fiuger into the ear. A sound is then per- 

 ceived, which resembles most nearly that of carriages at a 

 great distance passing rapidly oyer a pavement. 

 which does not The rapidity of the motion varies according to the degree 

 pressure on of force, with which the finger is retained in its place. The 

 thntympa- sound thus perceived is not at all dependent on the degree 

 OS pressure upon the tympanum ; for, on the contrary, the 

 vibratory sound is most distinct, when this pressure is slight, 

 if the linger be at the same tia;ie rendered rigid by the for- 

 cible ai'tion of antagonist muscles; iand when the ear is 

 stopped with great force without the presence of muscular 

 action, no such sound is produced. For instance, if the head 

 be rested upon the hand in such a position, as to press w'fth 

 its whole weight upon the ball of the thumb applied to the 

 ear, no noise is perceived, unless the extrennty of the thumb 

 be at the some time pressed against the head, or unless the 

 action of some other muscles be communicated to the ear, 

 by any inadvertence in the method of conducting the expe- 

 ti.nctjt. 



When 



num. 



