ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 141 



generally lasts twice as long as the same movement excited by a 

 single induction shock." V. Kries confirmed this, and was also 

 able to show from the graphic record of the activity of the flexor 

 muscles, with the quickest possible rhythmical movements of the 

 middle finger or whole hand (9 per sec.), minute but quite 

 visible oscillations, accessory to the larger waves, with an interval 

 of -^g- sec. (Fig. 62, &). 



If every experimental error from mechanical vibration is here 

 really excluded, we must inevitably conclude with v. Kries that 

 the rhythm of increase in the muscle, as in other cases, indicates 

 the rhythm of the central impulses that impinge upon it. With 

 a rapid sequence of short movements we should therefore have to 

 picture the process of innervation as such " that our will presides 

 over combinations of stimuli in which the single impulses follow 

 with great rapidity, one predominating in each case over the rest 



FIG. 62. Oscillations with voluntary muscle activity, a, With strenuous, persistent contraction 

 of muscles of the forearm (hand balled towards the list) ; the spring rests on the volar side 

 of the under-arm. I, Activity of flexor muscles on rapid rhythmic bending of the middle- 

 finger, (v. Kries.) 



to a marked extent." The extent and diversity of physiological 

 reaction in quick and sluggish muscle, as above, are closely allied 

 to the idea that along with slow and rapid movements there is 

 also innervation of functionally different elements, the more so as 

 partial innervation of one and the same muscle does undoubtedly 

 occur. In favour of such a view, which needs much farther 

 investigation, we may perhaps quote the observation of v. Kries 

 that the highest frequency of motor impulses occurs, not with the 

 development of the greatest power, but with the greatest mobility. 

 " The most pronounced efforts were produced with low stimulation- 

 frequency (10 12 per sec.)." If these last experiments militate 

 against the theory that there is a constant invariable " intrinsic 

 rhythm " of the central nervous system, this is no less the case 

 in v. Limbeck's observations on the number of oscillations yielded 

 by a muscle on artificial excitation of the brain or spinal cord by 

 induction currents of alternating frequency (30). Both in warm- 



