FAST AND SLOW RECORDS OF FATIGUE 
209 
possible gradations between the extremes, and these may possibly 
be explained upon the basis of differences of irritability and 
responsiveness of the “tonic” and “contractile” substances in the 
muscle. 
By the use of the chronometer relative duration times of the 
various phases are easily calculated in terms of the fast drum 
method. From data taken, for example, latency, contracture and 
relaxation lie roughly between 0.005 and 0.02 ; 0.04 and 0.2 ; and 
0.02 and 1.0 second, respectively. 
By proper signal device count can be kept and any response 
can be located at will, on curves by either method. 
Department oE Zoology, 
Iowa State College. 
