540 MOVEMENTS. 



The duration of the electric current applied to the nerve is only 0"'0008. Contrac- 

 tion, however, does not follow immediately, there being an interval, called pose, of about 

 one-fiftieth of a second. The contraction then follows, which is succeeded by gradual 

 relaxation, the former being a little longer than the latter. This description represents 

 the contraction of an entire muscle, but it does not indicate the changes in form of the 

 individual fibres, a point much more difficult to determine satisfactorily. It is pretty 

 well established, however, that a single fibre, with its irritability unimpaired, becomes 

 contracted and swollen at the point where the stimulation is applied. Now, the question 

 is whether, in normal contraction of the fibres in obedience to the natural nervous stimu- 

 lus, there be a uniform shortening of the whole fibre, a shortening of those portions only 

 that are the seat of the terminations of the motor nerves, or a peristaltic shortening and 

 swelling, rapidly running the length of the fibre. 



The recent experiments of Aeby, which have been repeated and extended by Marey, 

 demonstrate beyond a doubt that, when one extremity of a muscle is excited, a contrac- 

 tion occurs at that point and is propagated along the muscle in the form of a wave, ex- 

 actly like the peristaltic action of the intestines, except that it is more rapid. Both Aeby 

 and Marey have succeeded in measuring the rapidity of the wave, and they find it to be 

 about forty inches per second. Applying this principle to the physiological action of 

 muscles, Aeby advances the theory that shortening of the fibres takes place wherever a 



stimulus is received, and that 

 this is propagated in the form of 

 a wave, which meets in its course 

 another wave starting from a dif- 

 ferent point of stimulation. As 

 we know that the motor nerves 

 terminate at different points by 

 becoming fused, as it were, with 

 the sarcolemma, we can readily 

 comprehend, under this theory, 

 how the simultaneous contrac- 

 tion of all the fibres of a muscle 

 is produced by stimulation of its 

 motor nerve. This idea is ex- 

 pressed in the accompanying dia- 



FTG. 160. Diagram of the muscular icave. (Aeby.) gram. Although this view of the 



physiological action of the mus- 

 cular fibres is extremely probable, it cannot be assumed that it has been absolutely 

 demonstrated ; but it is certainly more satisfactory and better sustained by experimental 

 facts than any theory that has hitherto been advanced. 



Mechanism of prolonged Muscular Contraction. By a voluntary effort we are able 

 to produce a muscular contraction of a certain duration, and of a power, within certain 

 limits, proportionate to the amount of force we may desire to produce ; but, after a cer- 

 tain time, the muscle becomes fatigued, and it may become exhausted to the extent that 

 it will not respond to the normal stimulus. This is the kind of muscular action most 

 interesting to us as physiologists. 



The experiments of Marey seem to show precisely how far the nervous action that 

 gives rise to a powerful and continuous muscular contraction can be imitated by elec- 



nty. Calling the movement produced by a single electric discharge, secousse, which 

 we have translated by the word spasm, he calls the persistent contraction, tetanus. We 

 shall adopt this name to distinguish persistent muscular action from the single contrac- 

 tion that we have just described. 



It is a curious fact that a continued current of galvanic electricity passed through a 



