ELEMENTARY EXPERIMENTAL PHYSIOLOGY 



49 



A further experiment with curare can be made, (ii) The cerebral 

 hemispheres of a frog are destroyed, and then the sciatic nerves are 

 carefully exposed in each thigh ; a strong ligature is passed under the 

 sciatic nerve of one side, A, and is tied tightly around all the structures 

 of the thigh except the nerve. The circulation of the blood is thus com- 

 pletely stopped in the structures below the ligature. Stimulation of 

 either sciatic nerve produces a contraction of the muscles of the corre- 

 sponding leg. Under the skin of the back of the frog are injected two 

 or three drops of a 1 per cent, solution of curare. The poison is 



Fio. 50. Diagram of the experiment on the action of curare. 



absorbed by the blood-vessels and is circulated in all parts of the body 

 except those below the ligature. Paralysis is produced, and the frog 

 lies in a toneless condition and does not move if its toes be pinched. 

 Stimulation of the sciatic nerve produces in the case of the ligatured 

 leg, A, a contraction of the muscles, but in the case of the other leg, B, 

 no contraction occurs. The muscles, however, of the leg, B, contract 

 on direct stimulation. 



Both nerves in their upper portions have been exposed to the poison, 

 the muscles of both legs respond to direct excitation, but the ligatured 

 leg alone to indirect stimulation. The ligature has prevented the 

 poison from reaching the terminations of the nerves inside the muscles. 

 It is upon these terminations that the curare acts. 



The independent excitability of muscle can also be shown in the case 

 of cardiac muscle. The apex of the ventricle of the frog's heart con- 

 tains no ganglia, but it responds to a stimulus, and under appropriate 

 conditions will even contract rhythmically. 



Further experiments upon the independent excitability of muscle are 

 given in the advanced part of the course (p. 315). 



lr This operation should be performed with a pair of Spencer- Wells pressure- 

 forceps in order that no blood may be lost. 



D 



