16 



record the results which follow making and breaking the 

 current. 



Now reverse the direction of the current by meaus of the 

 commutator, so as to make the pole over the muscles the 



Dis)i of 

 m Salt Sol' 



Flat* lech-ode 



Fio. 9. 



anode, and again study the effects of strong, medium, and 

 weak currents at making and breaking. 



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. 



V. What happens to a Muscle when made to Contract ? 

 Examine the biceps muscle when the forearm is flexed, and 

 formulate the results of your observations. 



A. Extent of Contraction. 



With the hand in supinationand the arm semiflexed, measure 

 the length of the biceps. Now flex the forearm to a small 



