32 



ELEMENTARY PHYSIOLOGY. IV. 



the same duration. In this way take a series of tracings, 

 6 to 8 in all, with the rod shorter and shorter, shorten- 

 ing it less and less each time. Observe the gradual 

 fusion of a series of single contraction curves into the 

 curve of tetanus. 



Finally remove the oscillating rod and mercury cup 

 and arrange the apparatus for currents of rapid rhythm 

 (tetanisiiig currents) (cp. p. 11) and stimulate. A com- 

 plete tetanus is obtained. 



3. a. Connect in one circuit the cell, an in- circuit key, a beating 

 metronome, and a time-marker (Fig. ]4). 



Fig. 14. 



The metronome consists of an oscillating pendulum which (at each 

 oscillation) makes and breaks an electric current led to two mercury 

 cups. The period of oscillation can be changed by shifting a weight 

 along the pendulum so as to give oscillations at rates varying from 

 40 to 200 per minute. 



Arrange the metronome to beat once a second, and by means of 

 the time-marker, record periods of one second duration on the 

 running drum. 



b. Instead of the beating metronome a clock may be used to 

 make and break the circuit, or a chronograph, i.e. a small clock 

 with a recording lever may be brought to bear directly on the 

 running drum. 



With compasses measure the length on the drum of a period of 

 one second, and count in the tracing which just fails to be a com- 

 plete tetanus the number of oscillations per second of the muscle. 



