iv ELECTROMOTIVE ACTION IN MUSCLE 413 



tails. We may also refer to the observations of Klihne (50) 011 

 muscles treated with NH 3 vapour, and strongly contracted, 

 which still exhibited very striking secondary effects, when all 

 trace of movement had been abolished. This occurred on making 

 a new section, which implies that there may still be effective 

 waves of excitation in the muscle without any subsequent con~ 

 traction wave. Similar experiments on the adductor muscle of 

 the crab's claw (Biedermann) will be referred to below. 



Fano and Fayod made the important observation that the 

 " electrical pulse " of the auricle in the tortoise heart may even 

 increase when immobilised by tension ; this recalls the striking 

 effect of tension on all muscular processes, in regard no less to 

 mechanical yield of work than to thermic relations. In this con- 

 nection, too, is the beneficial effect of tension in normal striated 

 muscle upon secondary activity (51). Meissner and Cohn observed 

 that with indirect excitation of the muscle the secondary (exciting) 

 effect increased when the primary muscle was tetanised during 

 tension. Even in single twitches this is easily demonstrated 

 on muscles in which the excitability has perceptibly diminished. 

 The latter is a sine qua non, because experience shows that with 

 high excitability of the primary preparation, the secondary twitch 

 will reach its maximum with even low excitation. At a certain 

 stage of exhaustion, e.g. after long heating, it is found that the 

 capacity of giving secondary contractions when unloaded is en- 

 tirely lost by the muscle (gastrocnemius of H. temporaria), 

 although even a weak excitation from the nerve will produce 

 strong primary contractions. Even with strong excitation, and 

 highly sensitive secondary preparations, the latter are not affected. 

 In every case the secondary efficiency of the primary heated 

 muscle is restored immediately after loading, or any kind of 

 tension, to disappear again as soon as the strain is removed. 

 Up to a certain limit, the magnitude of the secondary 

 twitch increases with the load, but soon becomes maximal, 

 and it cannot be prima facie determined whether the factors 

 which produce such a marked augmentation of secondary 

 activity during extension increase it still further with constant 

 increase of loading. In the parallel-fibred sartorius also this 

 effect of tension may be elegantly demonstrated. Since we 

 cannot doubt that the secondary action of a muscle upon the 

 superposed nerve of another preparation is induced solely by 



