GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 113 



a remarkable degree the fact that at any given time the muscle has a definite 

 capacity for work. A suitable explanation of this is lacking. The corre- 

 spondence in the height of the contractions of the same group, and the differ- 

 ence in the height of different groups of contractions, must be attributed to the 

 existence within the muscle-cell of some automatic mechanism which regulates 

 the liberation of energy and which has its activity greatly influenced by the 

 alterations which result from action. Whether this supposed automatic regu- 

 latory mechanism controls both the preparation of the final material from 

 which the energy displayed by the muscle is liberated, and the amount of the 

 explosive change which results from the application of the irritant, cannot be 

 definitely said. 



(2) Effect of Frequent Excitations upon the Form of Separate Contractions. 

 The effect of activity is not only observable in the change in the height 

 of the muscular contractions, but in the length of the latent period, in the rate 

 at which the muscle shortens, and, above all, in the rate at which the muscle 

 relaxes. The effect of a large number of separate contractions, made in quick 

 succession, upon the rate at which the muscle changes its form during contrac- 

 tion, is illustrated in the myograms reproduced in Figure 44. 



FIG. 44. Effect of excitation upon the form of separate contractions. In this experiment the records 

 of the muscular contractions were taken upon a rapidly revolving drum. The muscle was the gas- 

 trocnemius of the frog ; the contractions were isotonic ; the weight was very light, about 10 grams ; the 

 stimuli were maximal breaking induction shocks ; and the rate of stimulation was twenty-three per 

 minute. 1 marks the first contraction ; 2, the 100th ; 3, the 200th ; 4, the 300th. The muscle was excited 

 automatically by an arrangement carried by the drum, and the excitation was always given when a 

 definite part of the surface of the drum was opposite the point of the lever which recorded the con- 

 tractions. 



In Figure 44 only the 1st, 100th, 200th, and 300th contractions were re- 

 corded. The perpendicular line marks the point at which the stimulus was 

 given. In this experiment the latent period for each of the succeeding con- 

 tractions is seen to be longer ; the height is lessened ; the rise of the curve of 

 contraction is slowed and the curve of relaxation is even more prolonged. These 

 and certain other changes are to be observed in the records of Figure 45, which 

 were taken in an experiment made under the same conditions as the last, except 



