MUSCLE-NERVE. 



IX. DIRECT IRRITABILITY OF MUSCLE; ACTION or CURARE. 



Inject into the dorsal lymph sac of a frog a few drops, about one- 

 half cubic centimetre of a one-per-cent solution of curare. First, 

 however, dissect out one sciatic nerve, passing a ligature under it 

 and tying it tightly about the thigh. All of the frog except that por- 

 tion below the ligature will come 

 under the influence of the drug 

 (see Fig. 10). In fifteen or twen- 

 ty minutes the drug action should 

 be complete. Make two sciatic- 

 gastrocnemius preparations, one 

 of the curarized side and one of 

 the non-curarized side. Set up 

 the inductorium for tetanizing 

 currents. Attach muscles to 

 myograph levers for recording. 

 Stimulate nerve of curarized side. 

 Result? Stimulate the nerve 

 of the non-curarized side. Re- 

 sult ? Stimulate the muscle of the 

 curarized side directly. Result ? 



What is the action of curare, 

 as deduced from these observations? Is the muscle fibre itself 

 directly irritable, aside from its nerve ? 



In the experiment under electrical stimulation, it was demon- 

 strated that, up to a certain point, the height of a single muscle 

 twitch is in direct proportion to the strength of the stimulus; i.e., 

 a minimal stimulus is accompanied by a minimal contraction and 

 a maximal stimulus by a maximal contraction. This will be com- 

 pared, later, with the action of heart muscle under similar circum- 

 stances. 



X. INFLUENCE OF LOAD ON MUSCLE TWITCH. 



When the weight is continuously supported by the muscle, both 

 when at rest and when contracting, the muscle is said to be loaded. 



FIG. 10. Curare Experiment, i, 

 Ligature around thigh ; j, sciatic nerve, 

 not included in ligature. Shaded area, 

 affected by curare; non-shaded area, 

 unaffected by curare. 



