36 



PRACTICAL PHYSIOLOGY 



mutator, 1 so as to make the pole over the muscles the anode, and 

 again study the effects of strong, medium, and weak currents at 

 making and breaking. 



Co mm uiaior Flat 



FIG. 26. Electrical Stimulation of Muscle through Skin. 



Record the results obtained on the following table : 



and arrange them according to their relative effectiveness. 



Compare them with the results previously obtained on the 

 isolated nerve-muscle of the frog (p. 33, I.). 



The difference between the effects of stimulation of a nerve 

 through the skin and those which follow stimulation with the 

 electrodes directly applied to it along its course is due to the fact 

 that in stimulating through the skin the current passes not along 

 but across the nerve, so that at the same point one side is under the 

 influence of the poles placed above it and the opposite side under 

 the influence of the other pole (Fig. 27). 



(Read Electrical Stimulation of Nerve in Text Book.) 



THE PASSAGE OF AN IMPULSE ALONG A NERVE 

 This may be investigated better after some practice in recording 

 the contraction of muscles, and it is taken in Lesson XI. 



F. WHAT HAPPENS TO A MUSCLE DURING 

 CONTRACTION ? 



Examine the biceps muscle when the forearm is flexed, and 

 formulate the results of your observations. 

 1 See Fig. 92, Appendix. 



