140 ELECTRO-PHYSIOLOGY CHAP. 



cerebral cortex fillet, or spinal cord, that the rate of muscular 

 vibration was much lower, the average of vibrations being only 

 10, when the stimulation -frequency was above 10 per sec.; 

 the results of voluntary, persistent contraction also correspond 

 with this lower value, and Canney and Tunstall (37) determined 

 the same in man (cf. also Griffiths, 38). 



V. Kries (39) arrived at similar results. He used apparatus 

 constructed after one of Marey's sphygmographs : " A steel spring- 

 plate is fixed at one end, the other free end carries on one surface 

 a wooden peg about 2 cm. long, to which is fastened the 

 little button a thin disc of wood 1 cm. in diameter that rests 

 on the muscle. The other surface of the steel spring is provided 

 with a sharp edge, which, as in Marey's sphygmograph, transfers 

 the movements of the spring, greatly magnified, to a very light 

 recording lever." When, after fixing the arm, the hand was bent 

 sharply towards the wrist, v. Kries obtained curves from the 

 flexor muscles of the under-arm like Fig. 62, r, with a distinct 

 rhythmical periodicity of 11 '8 per sec. The oscillations of the 

 other muscles were still slower, e.g. the deltoid (weight held out 

 with arm stretched horizontally) showed a rhythm of 9 '6 per 

 sec. ; plantar flexion of the foot only 7 '1. Hence it would 

 appear that the number of impulses hitherto taken as the rhythm 

 of central innervation, i.e. 1820 per sec., is too high, and that 

 with slow movements or persistent contraction it must, as a rule, 

 be estimated at 10-12 per sec. But as v. Kries pointed out, 

 both the rhythm of physiological innervation and the time- 

 relations of the single impulse must vary within considerable 

 limits, for the persistent contractions, due to voluntary innervation, 

 are effected by 1112 impulses per sec., while, on the other 

 hand, we are also capable of making 11 single movements in 

 a second (pianoforte playing), which rhythm must also necessarily 

 be present in the innervation process. It may be concluded 

 that in both cases notwithstanding the coincident periods the 

 innervation must have varied considerably (v. Kries, I.e.) 



As was remarked by Briicke (28), it is in the highest degree 

 improbable that voluntary muscular movements are due to only 

 one single efferent impulse from the cerebrum. In all cases, 

 even the shortest voluntary " twitch " implies a short tetanus. 

 This agrees with Barat's statement (14, p. 26) that "a voluntary 

 contraction of the simplest possible character (tap with the finger) 



