564 



THE DURATION OF A MUSCLE CONTRACTION. 



the muscle-poisons consists in their control of the imbibition of water by the 

 muscle-substance. As the muscular contraction depends on imbibition, the form 

 of contraction of the poisoned muscle will be influenced by the state of imbibition 

 produced in it by the poison. 



The contraction-curves of unstriated muscles are similar to those of striated 

 muscles, but the contraction takes place, after a latent period of as much as 

 several seconds, visibly later and more slowly. 



The contraction in a preparation of a frog's stomach lasts 600 times as long 

 as that of a striated muscle, and the latent stage amounts to 1.5 seconds. The 

 curve ascends more steeply than it descends, and its apex is flattened. Warming 

 increases the height of the curve, and shortens the latent period and the duration 

 of contraction; above 39 C., however, the conditions are reversed. 



A muscle contracted as a result of stimulation returns to its original length 

 only if a sufficient extending force is applied to it, as by weights suspended from 

 it. Otherwise it will remain somewhat shortened for a considerable time, the 

 resulting condition being designated contracture or contraction-remainder. This is 

 especially well marked in muscles that have been previously subjected to strong, 

 direct stimulation, or are greatly fatigued, or more strongly acid, or approaching 



FIG. 194. I, Contraction of a fatigued calf-muscle from the frog, recorded on a v: 



fork. Each dentation represents 0.01613 second; a b, latent irritation; b c, stage of increasing energy, c 

 stage of diminishing energy. II, The most rapid writing movement of the right hand, recorded on the vibrating 

 plate of a tuning-fork. Ill, The most rapid tetanic tremor-movement of the right forearm, recorded on the 

 same plate. IV, Myographic curve on closing and opening a current applied to the muscle itself (after Wundt). 



a condition of rigor, or have been obtained from animals poisoned with veratrin. 

 The phenomenon of contracture is also observed in man. 



In man, single twitching movements of the muscles may be executed with 

 great rapidity. The determination of the time-relations of such movements may 

 be made most simple by recording the movement in question upon the vibrating 

 plate of the tuning-fork. Fig. 194, II, represents the most rapid movement that 

 Landois could execute voluntarily with the right hand in writing the letters n n 

 in succession. Each ascending and descending part of the movement comprises 

 3.5 vibrations (i = 0.01613 second) = 0.0564 second. In III the right arm was 

 made to vibrate laterally to and fro on the tuning-fork plate in tetanic tremor; 

 here the to-and-fro movement comprised from 2 to 2.5 vibrations from 0.0323 

 to 0.0403 second. 



v. Kries found that a simple muscular contraction excited by an induction- 

 shock lasts longer than a single, momentary, voluntary movement. The direct 

 registration of the muscular thickening during a single voluntary contraction 

 shows that the contraction within the muscle lasts longer than the movement 

 developed in the passive motor organ itself. This shorter duration of the resulting 

 movement, which at first appears paradoxical, is due to the fact that, shortly 

 after the primary voluntary muscular contraction, a contraction of antagonists 

 takes place, and as a result a part of the intended movement is cut off. Even 

 with the most rapid voluntary movements in man, v. Kries found that about 



