GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 123 



tracture offers an internal support to the muscle, and raises the total height 

 of the contraction curve just as von Frey found an external support to do, 



can be seen in Figure 57. 



5. Effect of Gradually Increasing the Rate of Excitation. — One of the 

 most instructive methods of exciting tetanus is to send into the muscle a series 

 of breaking induction shocks of medium intensity, at a gradually increasing 

 rate. The record of such an experiment has been reproduced in Figure 56. 



Fig. 56.— Effect of a gradually increasing rate of excitation. Excitation of a gastrocnemius muscle 

 of a frog with breaking induction shocks of medium strength, The time was recorded directly, by a 

 tuning-fork making 100 vibrations per second. The rate of excitation was gradually increased, and 

 then gradually decreased. The ascending curve, n-b, shows the effect of increasimr, and the descending 

 curve, c-d, of decreasing the rate of stimulation. Excitation was given by means of a special mechanism 

 for interrupting the primary circuil of an induction apparatus and at t he same time short-circuiting the 

 making shocks. This interrupter was run by an electric motor Which was allowed to Speed lip slowly, 

 and was slowed down gradually. 



At the beginning of the experiment, a, one complete contraction with a 

 wave of elastic after-vibration was recorded j this was followed by two eon- 

 tractions of le.-s height, " introductory contractions ;" then came three contrac- 

 tions each of which was higher than the preceding, "staircase contractions;" 

 these were followed by three contraction.-, which, in spite .,1" the developing 

 contracture, were of less height, " fatigue effect" The rate of excitation at 

 this place was about 17 per second. From this point on, the developing con- 

 tracture supported the muscle more and more and the contraction waves became 

 less and less, until finally, when the rate had become ,"><! a second, the effect 

 of the separate stimuli could scarcely be detected, although the curve continued 

 to rise. This is as far as the record shows, but the rate was increased still 

 further, and the contraction curve continued to rise, although less and less, 



