472 



ACTION OF CURARA. 



[By means of the following arrangement we may prove that the terminal parts 

 of the nerve are paralysed. Ligature the sciatic artery of one leg of a frog, and 



then inject curara into a lymph-sac. After the 

 animal is fully poisoned, expose the sciatic 

 nerve in both legs, leaving all the muscles 

 below the knee-joint, then clean and divide 

 the femur at its middle. Pin a straw flag to 

 each limb, and fix both femora in a clamp, 

 with the gastrocnemii uppermost, as in fig. 

 316. Place the two nerves, N, on electrodes 

 attached to two wires coming from a com- 

 mutator, C (fig. 31 C). From the opposite 

 binding screws of the commutator, two wires 

 pass to the gastrocnemii. The other two 

 binding screws of the commutator are con- 

 nected with the secondary coil of an induction 

 machine ( 330). The bridge of the com- 

 mutator can be turned so as to pass the current 

 either through both muscles or both nerves 

 the latter is the case in the diagram (H). 

 When both nerves are stimulated, only the non- 

 poisoned leg (NP) contracts. Reverse the com- 

 mutator, and pass the current through both 

 muscles, when both contract.] 



[Rosenthal's Modification. Pull the secondary coil 

 far away from the primary, and pass the current 

 p t . through both muscles. Gradually approximate the 



j key ' ' secondary to the primary coil, and in doing so, it will 



' >' be found that the non-poisoned leg contracts first, 



but on continuing to push up the secondary coil, both limbs contract. Thus, the poisoned limb 



Fig. 316. 

 Scheme of the curara experiment. B, 

 battery ; I, primary, II, secondary 

 spiral ; N, nerves ; F, clamp ; NP, 

 non-poisoned 1 

 C, commutator 



Fig. 317. Fig. 318. 



Fig. 317. Curve showing the excitability in the sartorius of a frog in a normal and curarised 

 muscle. Fig. 318. Distribution of nerves in the sartorius of a frog and the curve of ex- 

 citability in different parts of the muscle, i.e., the excitability is greatest where there are 

 most nerve-endings. 



does not respond to so feeble a faradic stimulus as the non-poisoned one, a result which is not 

 duetto the action of the curara on the excitability of the muscle. The non-poisoned limb 



