370 THE WAVE OF MUSCULAR CONTRACTION. 



end of the muscle, so that they touch the muscular fibres close 

 to the end. 



Bring the levers to trace on the cylinder rotating on its 

 swiftest axis. While the two points of the lever are describ- 

 ing two parallel lines on the cylinder, send a single induction 

 shock through the lever. 



Each of the two levers will describe a curve, each curve in- 

 dicating the thickening of the muscle under the lever during 

 the contraction. But these curves will not be exactly one 

 under the other ; one, viz., that described by the lever nearer 

 the electrodes, will be a little earlier than the other. The dif- 

 ference in time between the commencement of the two curves 

 will be more marked in an exhausted muscle, or in a muscle 

 exposed to a low temperature, than in a fresh and very irri- 

 table muscle. 



Tin: contraction then does not take place in the whole fibre 

 at t/i<- xnme time, but travels with a certain velocity from the 

 point at which, the electrodes are placed along the fibre. 



Obs. III. Repeat the observation ; placing the electrodes on 

 the muscle close to the tendon of insertion instead of close to 

 the origin. 



The results are just the same; the wave of contraction 

 travels in either direction. 



Obs. IV. Instead of resting the levers on the muscle as di- 

 rected above, the muscle may be placed on a piece of cork 

 with holes in it and two slips of thin foil looped round two 

 distant parts of the muscle, each slip being connected with a 

 lever below, as in fig. 281. 



If the tuning-fork be brought to trace on the cylinder be- 

 low the levers, the interval of time between the commence- 

 ments of the two contractions may be exactly determined, 

 and the distance between the two levers on the muscle being 

 accurately measured, the velocity of the wave of contraction 

 mav be calculated. 



