IX.] PROPERTIES OF CONTRACTILE TISSUE. 99 



machine arranged for an interrupted current, 

 directly to the muscle. 



Observe that the current applied directly to 

 the muscle produces the same effect as when 

 applied indirectly through the nerve. To 

 completely eliminate the effect of stimu- 

 lating the nerves urari should be given to a 

 frog the brain of which has been destroyed. 

 Tetanize the muscle with currents of increas- 

 ing strength until it is completely exhausted, 

 pushing the secondary coil right up over the 

 primary. 



Cut the muscle across in half, with a quite 

 clean scalpel, and press on one section a piece 

 of faintly blue, on the other a piece of neutral 

 litmus paper. Both will be turned red where 

 they come in contact with the muscle. 



b. Dissect out the gastrocnemius from the leg 

 used in 1 6, and place it for five minutes 

 in normal saline solution heated to 50 C. 

 Observe that it has become contracted and 

 opaque, i.e. rigor mortis has set in. 



Cut the muscle across, and test with litmus 

 paper as in a. The muscle will be distinctly 

 acid, even more so than the tetanized muscle 

 in a. 



c. Take a fresh, living gastrocnemius from a frog 

 just killed, cut it across as in a and b, and 

 test the sections with neutral litmus paper. 

 The muscle will be found neutral or faintly 

 alkaline. 



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