MUSCULAR WORK. 569 



unstriated muscles and in the heart of only from 10 to 15 millimeters. 

 These figures, however, apply only to excised muscles, for in the striated 

 muscles of living human beings the rapidity of propagation is much 

 greater, namely from 10 to 13 meters. 



Method. For the demonstration of this motor phenomenon, Aeby placed a 

 writing-lever transversely across the origin of a muscle of considerable length 

 and another across its insertion. Both were raised by the thickening resulting 

 from the contraction of the respective parts of the muscle, and the movements 

 were recorded one above the other on the drum of a kymograph. If one ex- 

 tremity of the muscle is now stimulated, the contraction-wave that rapidly traverses 

 the muscle lifts first the proximal and then the distal lever. As the velocity 

 with which the drum revolves is known, the rapidity with which the contraction- 

 wave is propagated through the portion of muscle under examination can readily 

 be calculated from the distance between the elevations of the two levers. 



The time corresponding to the length of the abscissa of the curve in- 

 scribed by each recording lever is equal to the duration of the contraction 

 in that part of the muscle; according to Bernstein this is from 0.053 "to 

 0.098 second. By multiplying this value by the ascertained rapidity of 

 propagation of the contraction-wave through the muscle, the wave- 

 length of the contraction-wave is obtained; this equals from 206 to 380 

 millimeters. 



The rapidity and the height of the contraction-wave are diminished 

 by cold, fatigue, gradual degeneration, and some poisons. On the other 

 hand, the strength of the stimulus and the extent to which the muscle 

 may be weighted have no influence on the rapidity of the wave. In ex- 

 cised muscle the wave diminishes in size during its course through the 

 muscle, but not in the muscles of a living human being or animal. The 

 contraction-wave never passes from one fiber to an adjacent fiber; 

 neither does it leap over an interposed tendon or a transverse tendinous 

 septum. 



If a muscle of considerable length be stimulated locally at its middle, 

 a contraction-wave is propagated from the point of stimulation toward 

 both extremities, and in other respects possesses the properties pre- 

 viously described. If two or more points in the muscle are stimulated 

 at the same time, the wave-movement sets out from each, and one 

 may even pass over another. 



If a stimulus be applied to the motor nerve of a muscle, it will be 

 conducted to each muscle-fiber, whose contraction-wave must develop 

 at the motor end-plate and be propagated thence in both directions along 

 the fiber, which is only from 5 to 9 centimeters in length. In accord- 

 ance with the obvious inequality in the length of the motor fibers from 

 the nerve-trunk to the end-plates, the contraction will not commence at 

 absolutely the same moment in all of the muscle-fibers, as the conduction 

 through the motor nerves likewise occupies a certain amount of time. 

 The difference, however, is so small that the muscle, stimulated through 

 its nerve, appears to contract simultaneously as a whole. 



An absolutely simultaneous, momentary contraction of all of the 

 fibers of a muscle can occur only if all are stimulated at the same time. 



MUSCULAR WORK. 



The muscles are most perfect machines not only because they utilize 

 most completely the substances consumed in their activity, but be- 



