VOLUNTARY MUSCLE. 19 



short distance by hand, not more than 1 mm. Now carefully 

 move the coil toward the primary so that at each position 

 there is produced a slightly greater contraction than before. 

 Distinguish the "make" and "break" contractions on the 

 record by the letters nt and b placed beneath. Also designate 

 the position of the secondary coil. It is possible by carefully 

 increasing the stimulus to obtain a graduated series of con- 

 tractions from both the make and break shocks (Fig. 3). When 

 the series is complete, indicate the minimal and maximal 

 stimuli. 



Discuss the application of the all-or-none principle to your 

 records. 



INDEPENDENT EXCITABILITY OF MUSCLE. 



Ordinarily the question, as to whether a muscle could respond 

 if its nerves were absent, is of academic interest. But if we wish 

 to test the power of a muscle which has lost its voluntary function 

 by injury to the nerve, we find long after the nerve has degenerated, 

 that the muscle responds to direct electrical stimulation. It can 

 also be shown that with the nerve intact but with the connection 

 between the nerve and muscle paralysed, the muscle is still excit- 

 able. This can be done by the injection of the poison "curare" 

 into the circulation. After a few minutes has elapsed, stimulation 

 of the nerve no longer affects the muscle, while stimulation of the 

 muscle causes it to contract. From such experiments as these 

 it appears that muscle can contract without the mediation of 

 either nerve fibres or motor end plates. 



Experiment 5. The sciatic nerves are exposed in each leg of a 

 frog which has the brain destroyed. A ligature is passed under 

 one sciatic and around the thigh and tied tightly so as to 

 occlude circulation in that leg. A few drops of 1% curare 

 solution are injected into the back of the frog. From time to 

 time stimulate each sciatic nerve with induction shocks. In a 

 few minutes, the leg with intact circulation refuses to respond 

 or else responds very much less than the ligated leg. When 

 this stage has been reached stimulate the muscles of the un- 

 ligated leg directly. Their response demonstrates that the 



