134 AN AMERICAN TEXT- HOOK OF PHYSIOLOGY. 



rate of 8 to 12 per second, the average being 10. The rate of oscillations was. 

 quite independent of the rate of excitation, and oscillations of the same rate 

 were seen by voluntary and by reflex contractions. Tunstall 1 found by the use 

 of tambours, in experiments on voluntary contract ions of men, a rate of 8 to 13 

 per second, with an average of 10. Griffiths 2 likewise used the tambour 

 method, and studied the effect of tension on the rate of oscillations in voluntarily 

 contracted human muscles. He observed rates varying from 8 to 19, the rate 

 being increased with an increase of weight up to a certain point, and beyond this 

 decreased. The oscillations became more extensive as fatigue developed. Von 

 Kries by a similar method found rates varying witli different muscles, but 

 averaging about 10. 



It is not easy to harmonize the view that 8 to 13 excitations per second 

 can cause voluntary tetani, when it is possible for the expert pianist to make 

 as many as 10 or 11 separate movements of the finger in a second. It is, 

 indeed, a common observation that a muscle can be slightly and continuously 

 voluntarily contracted, and, at the same time, be capable of making additional 

 short rapid movements. Von Kries would explain this as due to a peculiar 

 method of innervation, while Biedermann favors Gruetzner's 3 view that the 

 muscle may contain two forms of muscle-substance, one of which is slow to 

 react, resembling red muscle-tissue, and maintains the continuous contraction, 

 the other, of more rapid action, being responsible for the quicker movements. 

 Although the evidence is, on the whole, in favor of the view that all normal 

 contractions of voluntary muscles are tetanic in character, there is a great deal 

 which remains to be explained. 



Effect of Artificial compared with Normal Stimulation. — Experiment shows 

 that, with the same strength of irritant, a muscle contracts more vigorously 

 when irritated indirectly, through its nerve, than when it is directly stimulated. 

 Rosenthal describes the following experiment : If the nerve of muscle A be 

 allowed to rest on a curarized muscle B, and an electric shock be applied in 

 such a way as to excite nerve A and muscle B to the same amount, muscle A 

 will be found to contract more than muscle B. 



Further, it has been found that muscles respond more vigorously to volun- 

 tary excitations than to any artificial stimulus which can be applied to either 

 the nerve or muscle. This shows itself, not only in the fact that a muscle can 

 by voluntary stimulation lift much larger weights than by electrical excitation, 

 but that after a human muscle has been fatigued by electrical excitations it 

 can still respond vigorously to the will. An illustration of this is given in 

 Figure f>8. 



Fatigue of Voluntary Muscular Contractions. — Mosso and his pupils have 

 done a large amount of work' upon the fatigue of human muscles when excited 

 by voluntary and artificial stimuli under varying conditions (see p. 72). The 

 results at which they arrived all favor the view that human muscles differ 

 but little from those of warm-blooded animals, and that the facts which have 



1 Journal of Physiology, 1886, vii. p. 114. 2 Journal of Physiology, 1888, ix p. 39. 



5 Pjluger\ Archiv, 1887, Bd. 41, S. 277. 



