RHEOSCOPIC LIMB. 199 



Rheoscopic limb. Secondary contraction. The nerve must 

 be freshly prepared. Dissect the second limb of the frog upon 

 which you have been performing the previous experiments, and 

 cut the nerve near the vertebral column. 



(a) Let the nerve fall upon its own muscle in such a manner 

 as to touch it in two points, one of which is near the middle 

 (equator) of the muscle and the other as far removed from it 

 as possible. 



A contraction will follow and will be repeated if the nerve 

 is very sensitive when it is lifted off again. Contraction without 

 metals. 



If the muscle does not contract make an artificial cross section 

 and let the second point of contact be the cross section. Defer 

 this second part until (b) and (c) have been concluded. By that 

 time the excitability of the end of the nerve may have disappeared 

 and it will be necessary to cut off the dead portion. 



(b) Place the rheoscopic nerve lengthways upon the first 

 muscle and stimulate the latter with interrupter shocks. The 

 rheoscope will respond to every contraction of the first limb. 



(c) Lay the nerve lengthways upon the ventricle of the frog's 

 heart, which is to be excised for the purpose and must be beating 

 vigorously. 



The cause in (a) is that the rheoscopic nerve connects two 

 points of different potential, and the current which passes 

 through the nerve stimulates it, and, secondarily, its own muscle. 

 In (b) and (c) the rheoscopic nerve lies along the path 

 of the electrical wave which courses down the contracting 

 muscle, and is thereby stimulated and its muscle contracts. 

 The rheoscopic limb acts as a highly sensitive current detector, 

 hence its name. 



Transmission of nervous impulses takes place in both 4 

 directions in the same nerve. Carefully dissect off the 

 muscles of the anterior surface of the leg, so as to include 

 the distribution of the peroneal nerve. 



