TETANUS 565 



consumed by the contraction. This increase in time falls very slightly on 

 the latent period, is more pronounced in the contraction phase, but is very 

 marked in the relaxation phase, figure 355. 



FIG. 355. Contractions of the Gastrocnemius Muscle to Show Fatigue. The numbers 

 printed on the figure indicate the contraction in the series which is recorded. (Lee.) 



13. The Effect of Temperature on the Time of the Simple Con- 

 traction. Repeat Experiment 10 but record the contractions by the method 

 described in Experiment 1 1 above, recording a contraction for every change 

 of 5 C. Measure the time and amplitude of the different contractions, 

 and the phases of the simple contractions, and tabulate them as shown in 

 Experiment n. 



14. Tetanus. A continued contraction of a voluntary muscle can 

 be shown to be a fusion of simple muscle contractions. This is called a teta- 

 nus. Arrange the induction coil for stimulating with a series of rapidly 

 repeated stimuli. Set the secondary coil so the break inductions only will 

 stimulate thus securing one stimulus per vibration of the tetanometer key. 

 The rate of the stimulation is obtained from the Harvard tetanometer, a form 

 of key for rapidly interrupting the current, which should be connected with 

 the primary coil instead of the key, K, figure 350. Prepare a muscle-nerve 

 in the moist chamber and stimulate the muscle at a rate of 10 per second, 

 record the contractions on the drum moving at a speed of about 2 cm. per 

 second. Use care not to overfatigue the muscle, i.e., stimulate it only 2 sec- 

 onds at a time controlling the time by the extra key in the primary circuit. 

 Repeat this test, increasing the rate of stimulation each time by 5, that is 

 stimulate at 10, 15, 20, etc., per second. In the first stimulation there will be 

 a series of simple contractions with almost complete intervening relaxations. 

 As the rate is increased these relaxations become less and less until presently 

 a rate is found which produces continuous, apparently uninterrupted contrac- 

 tions. This is a tetanus. The others are incomplete tetani. The frog's 

 gastrocnemius at a temperature of 20 C. is tetanized with a stimulation 

 of from 25 to 30 per second. 



