connected through a double key with the >ec< >ndarv of an induc- 

 lorium. Make a nerve muscle preparation, preserving the full 

 lent/tit nf the sciatic iier:-e, and place in the in i-t chamber with the 

 electrodes under the nerve and as far apart a- possible. With a 

 tuning fork and signal magnet pressed against the drum. >timulate 

 with a maximal make shock and record the latent period and con- 

 traction (as in exp. \<)\ ). fii'ft. with the electrode far trom the 

 muscle in circuit, and then with the near electrode in circuit. 

 The time differences in the latent periods inn-i be the time required 

 for a nerve impulse to pass along a space equal to that between the 

 tuo cath: des (why?). Measure this distance and calculate the 

 rate of the nerve impul-c per second. 



213. The salt <>f fatii/nc. Pith the brain of a frog (but not 

 the spinal cord ) and plug the cavity with cotton to prevent bleeding. 

 Kxpose the sciatic nerves of both sides and pass a thread under- 

 neath so that they may be lifted readily for stimulation. Stimulate 

 the right sciatic (with a current strong enough to cause contraction 

 of the left leg) and note the time required for the muscles of the 

 left leg to relax, completely fatigued. Have the right leg muscles 

 also relaxed? Call this time A. Then stimulate the left sciatic 

 (do not fatigue it) to see if the muscles still contract. Result? 

 \Yhcre has fatigue occurred? (Juickly remove the skin from the 

 right leg. tie the thread about the sciatic and cut centrally to the 

 ligature, remove the muscles fn in the thigh, cut the femur and 

 fasU-n in a clam]). Stimulate the sciatic with a weak stimulus 

 i tciani/.ing ) until fatigue occurs, recording the time required. Call 

 this time \\. Xow stimulate the muscle directly until fatigued. Call 

 this time C. What ha- been fatigued here? 



To prove that the sciatic nerve has not been fatigued at the 

 point of stimulation proceed as tollow-: Remove the left leu;. 

 rcttiiiiiiH/ the <\7/<'A' leiit/tli of the sciatic ncn'c. and place in a lemur 

 clamp witli the nerve across non-polarizable electrode- near the 

 muscle. A galvanic current ( from desk electrodes) is to be passed 

 through the nerve in order to block the nerve impulse, and the far end 

 of the nerve i- stimulated with a weak tetanixing current \< r a 

 length of linn/ equal to A -J- B -f- C. If the muscle contracts when 

 the polarixing current i- turned off. but the tctani/ing stimuli arc 

 -till given, we can >afelv assume that no tatigue has occurred at the 

 part of stimulation during the time of the experiment. Which are 

 fatigued in order in this experiment nerves, nerve endings, nerve 

 cells, muscle liber? 



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