334 THE OUTGO OF ENERGY 



the right the screw at the top of the sleeve bear- 

 ing the recording drum until the sleeve is raised 

 from the friction bearing. The drum can now 

 be "spun." Start the tuning fork vibrating, 

 spin the drum, lay the writing point of the tun- 

 ing fork on the smoked paper near the line 

 traced by the electro-magnetic signal, and stim- 

 ulate the muscle with a maximal .induction 

 current. 



An interval will be found between the moment 

 of stimulation (marked by the electromagnetic 

 signal) and the beginning of contraction. This 

 interval is the mechanical latent period. Meas- 

 ure its duration by means of the tuning fork 

 curve. Measure also the duration of the period 

 of rising energy and the period of sinking energy. 



Helmholtz, who first measured the latent period 

 of frog's muscle, found a mean duration of 0.01 

 sec., while the phase of rising energy measured 

 0.04 sec., and the phase of sinking energy 0.05 

 sec. More recent measurements by Tigerstedt 

 and others have reduced the latent period 

 given by Helmholtz to from 0.0025 to 0.005 

 sec. The interval observed grows less as the 

 intensity of stimulation is increased from the 

 threshold to the maximal value ; further in- 

 crease in intensity (supermaximal stimulation) 

 causes no further diminution in the latent period. 



