26 



ELEMENTARY PHYSIOLOGY. III. 



key in the secondary circuit, close the knock-down key, 

 open the key in the secondary circuit; turn the pulleys 

 by hand, making the movement as slow as possible as 

 t^e rod touches the knock-down key, so that the tracing 

 of the contraction and of the relaxation of the muscle 

 make a single line. This marks the moment in the myo- 

 gram at which the nerve was stimulated, and there is a 

 space between this and the beginning of contraction. 

 The time taken by the drum in passing over this space 

 is the latent period. (A similar curve may be taken 

 higher on the drum with a load of 10 grams instead of 

 2 grams.) 



4. Time measurement of the parts of the curve. 



a. This may be taken by means of a broad steel band 



G_ 



Fig. 11. 



(Fig. 11), the rate of vibration of which has been deter- 

 mined. Place it so that the writing point is close under 



