158 EXPERIMENTAL PHYSIOLOGY. 



nerves. Apparatus. Daniell's cell, induction machine, two keys, 

 five wires, shielded electrodes, scissors, fine-pointed forceps, fine 

 aneurism needle, or fine sewing needle fixed in a handle, with the 

 eye free to serve as an aneurism needle, fine threads, pithing 

 needle, 1 per cent, watery solution of curara in a glass-stoppered 

 bottle, fine hypodermic syringe or glass pipette, frog. 



(a.) Arrange the battery and induction machine for an 

 interrupted current with a key in the primary circuit, and a 

 du Bois key to short-circuit the secondary as in Lesson 

 XXVIII., 2). 



(6.) Pith a frog, destroying only its brain, and inject into 

 the ventral or dorsal lymph sac one or two drops of a 1 per 

 cent, watery solution of curara. The poison is rapidly 

 absorbed. At first the frog draws up its legs, in a few 

 minutes it ceases to do so, and will lie in any position in 

 which it is put, while the legs are not drawn up on being 

 pinched, and the animal lies flaccid and apparently para- 

 lysed. 



(c.) Place the frog on its back. Expose the heart, and 

 observe that it is still beating. Take care to lose no blood. 



(d.) Expose the sciatic nerve on one or both sides. 



(i.) Apply the shielded electrodes under them, and 

 stimulate the nerves with tetanising shocks. There is no 

 contraction. 



(ii.) Apply the electrodes to the muscles, they contract. 



TJierefore, curara has paralysed Hie voluntary motor nerves, but 

 not tlie muscles. 



2. On what part of the Nerve does the Curare act ? 



(a.) Keep the induction apparatus as in the previous ex- 

 periment. 



(6.) Pith a frog, destroying only its brain. Carefully expose 

 the sciatic nerve and the accompanying artery and vein on 

 one side, e.g., the left, taking great care not to injure the 

 blood-vessels, which are to be carefully isolated for a short 

 distance with a finder. Thread a fine aneurism needle with 



