488 EFFECT OF VARIOUS CONDITIONS ON MUSCULAR CONTRACTION. 



propagated in a wave-like manner through the whole length of the muscle, until 

 it reaches its other end. The condition of excitement or molecular disturbance is 

 communicated to each successive part of the muscle, in virtue of a special conduc- 

 tive capacity of the muscle. The mean velocity of the contraction-wave is 3 to 4 

 metres per second in the frog (Bernstein, 3'869 metres) ; rabbit, 4 to 5 metres 

 {Bernstein and Steiner) ; lobster, 1 metre (Fridericq and van de Velde) ; in smooth 

 muscle and in the heart, only 10 to 15 millimetres per second ( 58, 4). These 

 results have reference only to excised muscles, the velocity of transmission being 

 much greater in the voluntary muscles of a living man, viz., 10 to 13 metres (Her- 

 mann, 334, II.). 



Methods. Aeby placed writing-levers upon both ends of a muscle, the levers resting trans- 

 versely to the direction of the muscular fibres. The muscle was stimulated, and both levers 

 registered their movements, the one directly over the other on a revolving cylinder. On stimu- 

 lating one end of the muscle, the lever nearest to this point is raised by the contraction-wave, 

 and a little later the other lever. When we know the rate at which the cylinder is moving, 

 and the distance between the two elevations, it is easy to calculate the rapidity of transmission 

 of the contraction-wave. 



Duration and Wave-Length. The time, corresponding to the length of the 

 abscissa of the muscle-curve inscribed by each writing-lever, is equal to the dura- 

 tion of the contraction of this part of the muscle (according to Bernstein, 0'053 to 

 0*098 second). If this value be multiplied by the rapidity of transmission of the 

 muscular contraction-wave, we obtain the wave-length of the contraction-wave 

 ( = 206 to 380 millimetres). 



Modifying Influences. Cold (fig. 337), fatigue, approaching death, and many 

 poisons [veratrin, KCy] diminish the velocity and the height of the contraction- 

 wave, while the 

 strength of the stim- 

 ulus and the extent 

 to which the muscle 

 is loaded are without 

 any effect upon the 

 velocity of the wave 

 (Aeby). In excised 

 muscles, the size of 

 the wave diminishes 

 Fig. 337. as it passes along the 



Upper two curves, 2 and 1, obtained from a rabbit's muscle by the muscle, but this is 

 above arrangement ; the lower two curves from the same muscle, not the case in the 

 when it was cooled by ice. muscles of Uving men 



and animals. The contraction-wave never passes from one muscular fibre to a 

 neighbouring fibre. 



[Fig. 337 shows the effect of cold on the muscles of a rabbit, in delaying the contraction- 

 wave. There is a longer distance between 1 and 2 in the lower than in the upper curves.] 



2. If a long muscle be stimulated locally near its middle, a contraction-wave is 

 propagated towards both ends of the muscle. If several points be stimulated 

 simultaneously, a wave movement sets out from each, the waves passing over each 

 other in their course (Schif). 



3. If a stimulus be applied to the motor nerve of a muscle, an impulse is com- 

 municated to every muscular fibre ; a con traction- wave begins at the end-organ 

 [motorial end-plate], and must be propagated in both directions along the muscular 

 fibres, whose length is only 3 to 4 centimetres. As the length of the motor fibres 

 from the nerve-trunk to where they terminate in the motorial end-plates is unequal, 

 contraction of all the muscular fibres cannot take place absolutely at the same 

 moment, as the nerve impulse takes a certain time to travel along a nerve. 



