634 A MANUAL OF PHYSIOLOGY 



freely in the sacral plexus and the spinal cord. Further, if the 

 nerve of the ligated leg be prepared as high up above the 

 ligature as possible, where the curara must undoubtedly have 

 reached it (just above the ligature the nerve has been isolated 

 and the circulation in it more or less interrupted), stimulation 

 of it will cause contraction of the muscles of the limb ; while 

 excitation of the other sciatic is ineffective. 



It can be also shown, by means of the negative variation or 

 current of action (p. 719), that a nerve-trunk on which curara 

 has acted remains excitable, and capable of conducting the 

 nerve-impulse. The conclusion, therefore, is that the curara 

 paralyzes neither nerve-fibre nor the contractile substance of the 



FIG. 221. FROG'S MOTOR NERVE -ENDING (WILSON). 



A, B, C, three muscle-fibres. The medullated nerve a loses its medullary sheath 

 and breaks up on B at i. It gives off at 2 a large non-medullated branch, 

 which also breaks up on B. The nerve-endings send ultraterminal fibrillas to 

 A, B, and C, some of which were seen to end in small knobs. A separate non- 

 medullated nerve, n, is shown, which forms a small plexus on B, one fibre of 

 which penetrates to a lower plane than the other, and ends by forming a knob 

 under the sarcolemma. 



muscular fibre, but some link between the two. If the assump- 

 tion be made that the efferent medullated nerve-fibres within the 

 muscle, since they are anatomically similar to those in the nerve- 

 trunk till near their terminations, are similarly affected by curara 

 and it is a justifiable assumption the seat of the curara 

 paralysis must either be the nerve-ending or some mechanism, 

 physiological if not anatomical, interposed between the nerve- 

 ending and the contractile substance. Now, Langley has shown 

 that the contractions caused by the local application of dilute 

 nicotine solution to points of the skeletal muscles of the frog, 

 both in normal muscles and in muscles whose motor nerves and 

 nerve-endings have degenerated after section of the nerves, 



