PRACTICAL EXERCISES 787 



moisten one of the nerves between the electrodes and the muscle with a 

 mixture of equal parts of ether and alcohol, diluted with twice its volume 

 of water, to abolish the conductivity. Or put the mixture in a small 

 bottle, in which dips a piece of filter-paper. The projecting end of the 

 filter-paper is pointed, and the nerve is laid on the point. As soon as 

 it is possible to stimulate the nerves without obtaining contraction in 

 this muscle, proceed to tetanize both nerves till the contracting muscle 

 is exhausted. If the other muscle begins to twitch during the stimu- 

 lation, more of the ether mixture must be painted on the nerve. As 

 soon as the stimulation ceases to cause contraction in the non-etherized 

 preparation, wash off the mixture from the other nerve with physio- 

 logical salt solution, and soon contraction may be seen to take place in 



j-jg 279. Fatigue Curve of Skeletal Muscle: Gastrocnemius of Frog. Indirect 

 stimulation; taken with arrangement shown in Fig. 278 (p. 785). Time-tracing, 

 j$- ff of a second. 



the muscle of this preparation. This shows that the nerve-trunk is still 

 excitable. Now, both nerves have been equally stimulated, and there- 

 fore the exhaustion in the non-etherized preparation was not due to 

 fatigue of the nerve-fibres, but of something between them and the 

 contractile substance of the muscle. 



10. Influence of Veratrine on Muscular Contraction. Arrange a 

 drum as in Fig. 278. Pith a frog (brain only), expose the sciatic nerve 

 in one thigh, and isolate it for inch from the surrounding tissues. 

 Pass under it a strong thread, and ligature everything except the nerve. 

 Now inject into the dorsal or ventral lymph -sac a few drops of o-i per 

 cent, solution of sulphate of veratrine. In a few minutes make two 

 muscle-nerve preparations from the posterior limbs. First put the 

 preparation from the unligatured limb on the myograph plate. Lay 



