52 Prof. J. Burdon-Sanderson. Relation of Motion in Animals 



Bernstein's " negative Schwankung," we can accept all he says as to its 

 coincidence in time with the moment of greatest intensity of the pro- 

 cess by which chemical is transformed into mechanical energy — the 

 moment in the shortening of an unloaded muscle at which its rate of 

 change increases most rapidly. As regards the period of decline, it might 

 suggest itself that the return of each element to its previous state is in 

 every instance the expression of an anabolic process, not merely a 

 result of the cessation of the opposite process. The facts we are con- 

 sidering, however, lead us for the present to regard the whole varia- 

 tion as the concomitant of one and the same chemical process, and we 

 are confirmed in this view by the observation that, as Ave shall see im- 

 mediately, the modifications which the monophasic variation undergoes 

 under external or accidental conditions affect both stages equally. 



Of these conditions one of the most important is temperature, par- 

 ticularly when muscles which have been kept for some time in physio- 

 logical salt solution are used.* We have hitherto had in view the Sar- 

 toriiis which has been kept for some twenty-four hours, and is at the 

 temperature of about 10° C. By placing it in a cooled chamber at 

 a temperature some 6° C. lower, and allowing it to remain there until 

 it has acquired the temperature of its environment, its mode of re- 

 sponding is not changed, but only in its relation to time. In shortening, 

 it takes a longer time to attain its minimum length, and if its con- 



Photograph 5. 



traction is resisted, its period of effort is of longer duration. Conse- 

 quently it is able to do more external work in a single effort than 

 before, although it is not able to support a heavier weight or maintain 

 a greater tension in a continuous effort. Now all these modifications 

 depend, so far as I have been able to ascertain, on diminution of the 

 rate of propagation of the excitatory wave. As has been already 

 stated, we are able to measure this rate with great facility and accu- 

 racy. By alternately cooling and warming our chamber we can deter- 

 mine in any number of instances the change of rate which a difference 

 of 2°, 4°, or 6° C. produces, and compare the data so obtained with the 

 effects of the same changes on the duration of the monophasic variation 

 and on that of the mechanical effort which it accompanies. 



* ' Journ. of Physiol.,' vol. 23, p. 332. 



