VOLUNTARY MUSCLE 41 



tested muscle. The explanation is that the electrical changes 

 in the tested muscle are strong enough to initiate impulses in the 

 nerve of the rheoscopic preparation. However, due to the poor 

 condition of the rheoscopic nerve-muscle, the experiment frequently 

 fails. 



The sciatic-gastrocnemius preparation to be used as a rheoscope 

 should be taken from a very healthy frog and dissected out with 

 the greatest care. Abuse of the nerve may destroy its sensitiveness 

 so that a new preparation must be made. 



Experiment 15. Current of Injury. One end of a gastroc- 

 nemius muscle is cut across transversely. This and the rheo- 

 scopic preparation are placed side by side on a clean glass plate. 

 The rheoscopic nerve, near its muscle, is placed in contact with 

 the uninjured surface of the muscle to be tested, the rest of the 

 nerve being held apart by means of a glass hook. Now the tip 

 of the rheoscopic nerve is allowed to touch the injured surface 

 of the muscle to be tested. A contraction of the rheoscopic 

 muscle should result at the moment of the nerve's contact with 

 the injured surface. 



Current of Action. Two nerve-muscle preparations are laid 

 side by side on a glass plate. The nerve of the one which is to 

 serve as the rheoscope is placed lengthwise against the muscle 

 to be tested and is then lifted by a glass rod at its middle so 

 that it is in contact with the muscle only at both ends. The 

 nerve of the muscle to be treated is next stimulated by single 

 shocks. With each twitch the rheoscopic muscle should re- 

 spond. If the test muscle is tetanized, the rheoscopic muscle 

 should be tetanized. 



A secondary twitch can also be obtained by laying a freshly 

 prepared nerve upon a beating frog heart. The two regions of 

 contact for the nerves are the base and the apex, the middle 

 part of the nerve being held away from the contracting muscle 

 as before. Each beat should, produce a twitch of the gastroc- 

 nemius. 



