342 MOTION IN ANIMALS AND PLANTS. 



time it has been kept, subsiding at first abruptly, afterwards more 

 gradually, so that its whole duration (i. e. , to the summit of the elec- 

 trometer curve) amounts to f roui two to six hundredths of a second. 



The discoverer of the Reizwelle, Professor Bernstein, assigned to it 

 a verv different duration. "In every element of muscular structure 

 the variation lasts between one two-hundred-and-fif tieth and one three- 

 hundredth second, and coincides with the period of latent stimulation." 

 At first sight this statement seems irreconcilable with fact, but it is much 

 less so than it appears to be. We have only to assume that Bernstein's 

 method of estimating a small and transitory difference of potential 

 between two surfaces was not sufficiently delicate to enable him to 

 appreciate those which exist during the period of decline, and that 

 what he regarded as the duration of the whole variation was in reality 

 the duration of its summit only. However this may be, it is clear that 

 we may divide the period of variation into two parts, which we may 

 call, respectively, the initial rise and the decline, of which the latter 

 lasts eight to ten times as long as the former, and that we may regard 

 the first as a period of upset, the second as a period of restoration. 

 Taking the period of upset as equivalent to Bernstein's "negative 

 Schwankung,'' we can accept all he sa3^s as to its coincidence in time 

 with the moment of greatest intensity of the process by which chem- 

 ical is transformed into mechanical energj^ — the moment in the short- 

 ening 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 considering, 

 however, lead us for the present to regard the whole variation as the 

 concomitant of one and the same chemical process, and we are con- 

 firmed in this view by the observation that, as we shall see immedi- 

 ately, 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 

 Sartorius 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 

 responding is not changed, but only in its relation to time. In short- 

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

 contraction is resisted its period of effort is of longer duration. Con- 

 sequently 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 



iJourn. of Physiol., vol. 23, p. 332. 



