440 SCIENCE PROGRESS. 



obtained by the following simple device. The upward 

 movement of the isotonic lever is stopped by a suitable 

 mechanism so arranged that the stop can occur at any 

 desired interval after the record has begun. If this arrest 

 occurs before the contractile stress of the muscle has ceased 

 the lever will be held up against the stop ; if on the other 

 hand it occurs at the moment when the contractile stress 

 ceases, the lever must fall. Now if the stop is arranged so 

 that the lever falls immediately after its upward movement 

 has been arrested, it is found that this fall begins at a point 

 which is situated on the isotonic curve between m and drs 

 of a second before this curve has reached its maximum. 

 Hence contractile stress has ceased although the isotonic 

 lever continues to rise. 



A further modification of the method is that of keeping 

 the lever arrested and suddenly releasing it ; here the same 

 thing holds good, for if released before the contractile stress 

 is over it will rise, and in this way the duration of the 

 contractile stress may be determined. 



The isotonic record is thus, according to Kaiser, the 

 account of an untrustworthy historian, for it records other 

 things besides the contractile stress. These other things 

 are partly the movement of the lever due to its own momen- 

 tum and partly that due to the passive elastic swing of the 

 muscle itself. The twofold view of the muscle response 

 advanced by Schenk is thus, according to Kaiser, un- 

 supported by data derived from the muscle curves, what- 

 ever support it may receive from other sources. The 

 response is the sudden assumption by the muscle of a new 

 condition of elastic equilibrium and the subsidence of this is 

 not a second response to excitation but is dependent upon 

 the new condition coming to an end. 1 



Those who are acquainted with the methods employed 

 in physiological investigation are not likely to underestimate 

 the importance of the issues here raised, but even those 



1 The experimental data, together with the theoretical interpretations 

 advanced by the writers concerned, may be found in Schenk's papers, 

 Archiv /. d. ges. Physiol., vols. 50, 53, 55, 61, 63 and 65, and in Kaiser's 

 paper, Zeitschr. f. Biol., vol. 33, etc. 



