38 ELEMENTARY PHYSIOLOGY. V. 



the poles which are on the living muscle (cf. diagram, 

 Fig. 17, A). 



It is to be noticed that when the current is increased 

 to a certain degree the portion which enters or leaves 

 the living part of the axis cylinder near their junction 

 with the dead part becomes sufficient to set up a stimu- 

 lus (cf. Fig. 17, B) and contraction will be obtained both 

 at make and break with each direction of the current. 



A similar experiment may be made with the sartorius muscle. 



4. Fatigue. Arrange the apparatus for recording the 

 latent period (Less. III. 3). Fix one nerve-muscle pre- 

 paration in the muscle chamber, put a weight of 20 

 grams in the hole of the lever next the axle (i.e. a load 

 of 4 grams), and take a curve of a single muscle con- 

 traction showing the latent period. 



In the remainder of the experiment the lever must not 

 be shifted. Let the drum revolve half way round, and 

 with stationary drum, open and close the key in the 

 primary circuit 50 times, i.e. stimulate the muscle 100 

 times. Then take a tracing of another single contraction 

 using the knock-down key. 



Repeat as in the preceding paragraph about half-a- 

 dozen times. 



In the curves obtained note the change of form. The 

 most striking feature is the progressive and great pro- 

 longation of the period of relaxation; the physical con- 

 dition of the muscle is altered so that it is less extensible. 

 The rate of shortening is throughout slower; the extent 

 of the shortening is at first greater and then becomes 

 less and less. There is some prolongation of the latent 

 period. 



