120 



AX AMERICAN TEXT- BO OK OF PHYSIOLOGY. 



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 53, 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 



Fig. 52.— 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. 



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. 



It is- evident that the condition of contracture which is developed in a 

 rapidly stimulated muscle will tend to maintain a condition of continuous con- 



Fig. 53.— Effect of rapid excitations to produce tetanus. Experiment with a gastrocnemius muscle 

 of a frog, excited directly, with breaking induction shocks of medium strength, at the rate of 33 per 

 second. The weight was about 15 grams. The drum was moving much more slowly than in the pre- 

 ceding experiment. The time record gives fiftieths of a second. 



traction, there being no opportunity for the muscle to relax in the intervals 

 between the succeeding excitations. 



4. Explanation of the Great Height of Tetanic Contractions. — We have 

 now to seek an explanation of the fact that a muscle when tetanized will con- 



