GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 117 



form of contraction peculiar to contracture is itself seen to lessen as fatigue 

 becomes excessive. Both of these facts are illustrated in Figure 47, but are 

 more strikingly shown in Figure 48, in which a more rapid rate of excitation 

 was used. 



The record in Figure 48 shows many points of interest : a to 6, a rapidly 

 developing staircase, which is accompanied by a rising of the base line, which 

 indicates that contracture began to make itself felt from the moment the work 

 began ; b to c, a rapid and then a gradual fall in the height of contractions 

 due to fatigue effects; G to d, a rise in the top of the curve in spite of the 

 lessening height of the contractions, due to the increasing contracture ; d to e, 

 a gradual fall of the curve of incomplete tetanus, due to the effect of fatigue 

 on the contracture ; e, complete tetanus, but continued gradual decline in the 

 height of the curve under the influence of fatigue. 



The following experiment, Figure 49, differs from those which have preceded 

 it, in that the muscle, instead of being directly excited, was stimulated indirectly 

 by irritation of its nerve. Each shock applied to the nerve was represented 

 by a separate contraction process in the muscle. The experiment illustrates 

 well the combined effect of the staircase and the contracture to raise the height 



FIG. 49. Development of incomplete tetanus and contracture, by indirect stimulation. A gas- 

 trocnemius muscle of a frog was indirectly stimulated by breaking induction shocks, of medium 

 strength, applied to the sciatic nerve. The rate was about 8 per second, as shown by comparison of the 

 seconds traced at the bottom of the figure with the oscillations caused by the separate contractions. The 

 weight was somewhat heavier than in the preceding experiment. The drum was revolving much faster 

 than in the other experiments, hence the difference in the apparent duration of the contractions. 



of the contractions. On account of the more rapid rate of excitation, the 

 contracture came on more quickly than in the preceding experiments ; it did 

 not become sufficient during the few seconds that this experiment lasted to 

 prevent the separate relaxations from being seen, and an incomplete tetanus 

 was the result. 



In the experiment the record of which is given in Figure 50, the muscle was 

 directly stimulated, and the rate of excitation was rapid, 33 per second. Not 

 even this rate sufficed to cause complete tetanus, and the crest of the curve 

 shows fine waves, which represent the separate contractions the combined effect 

 of which resulted in the almost unbroken curve seen in the record. Had the 

 rate been a little more rapid, no waves could have been detected and the tetanus 

 would have been complete from the start. The effects of the staircase and con- 

 tracture are merged into one another, and a very rapid high rise of the curve 

 of contraction is the result. It is noticeable that the summit of the curve is 

 rising throughout the experiment, owing to the increasing contracture. 



