MUSCLE 55 



and in a short time the skeletal muscles are paralyzed. 

 That the seat of the paralysis is not the muscles themselves 

 is shown by their vigorous response to direct stimulation. 

 The 'block' is not in the nerve-trunk, nor above it in 

 the central nervous system, for the ligatured leg is often 

 drawn up that is, its muscles are contracted, although the 

 poison has circulated freely in the sacral plexus and the 

 spinal cord. Further, if the nerve of the ligatured 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 con- 

 traction 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 



FIG. 161. TONIC CONTRACTION OF MUSCLE DURING PASSAGE OK CONSTANT 



CURRENT. 



Two sartorius muscles of frog connected by pelvic attachments. Current from 12 

 small Daniell cells in series passed through their whole length. Current closed at m, 

 opened at b. Time trace, two-second intervals. 



or current of action (p. 630), that a nerve-trunk on which 

 curara has acted remains excitable, and capable of conduct- 

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

 the curara paralyzes neither nerve-fibre nor muscular fibre, 

 but the link between the two which we call the nerve- 

 ending. In coming to this conclusion, the assumption is 

 made that the nerve-fibres within the muscle, since they are 

 anatomically similar to those in the nerve-trunk till near 



