GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 135 



been ascertained by experiments upon cold-blooded animals, such as the 

 frog, can be accepted with but slight modifications for the muscles of man. 

 In the experiment recorded in Figure 58 we see the effect of repeated tetanic 



Fig. 58.— Voluntary excitations are more effective than electrical. The flexor muscles of the second 

 finger of the left hand of a man were excited first voluntarily, a, then electrically, a-b, and then volun- 

 tarily, b. The electrical excitation consisted of series of induction shocks, which were applied once 

 every two seconds, during about half a second, the spring interrupter of the induction coil vibrating 

 23 times per second. Each time the muscle contracted it raised a weight of one kilogram. Each of the 

 contractions recorded, whether the result of electrical or voluntary excitation, was a short tetanus. 



contractions, excited by electricity, to fatigue a human muscle. Normal 

 voluntary contractions, if frequently repeated, provided the muscle has to 

 raise a considerable weight, likewise cause fatigue. This was illustrated in 

 the experiment recorded in Figure 59. 



Fig. 59.— Effect of fatigue on voluntary muscular contractions. The flexor muscles of the second 

 finger of left hand were voluntarily contracted once every two seconds, and always with the utmost 

 force. The weight raised was four kilograms. 



It is doubtful whether, in an experiment such as is shown in Figure 59, the 

 loss of the power to raise the weight is due to fatigue of the muscles. It is 

 more likely that the decline in power is due to fatigue of the central nerve- 



