LESSON III 



MUSCLE AND NERVE (Continued) 



IRRITABILITY, CONDUCTIVITY, AND ELASTICITY OF MUSCLE. THE 

 POWER OF MUSCLE TISSUE IN RELATION TO THE CROSS-SECTION 

 AND ARRANGEMENT OF ITS FIBERS 



1. Independent Irritability of Muscle. Pith a frog and destroy its 

 brain without losing any blood. Immediately close the opening with 

 the pointed end of a match. Make a median in- 

 cision along the posterior surface of the left thigh. 

 Isolate the sciatic nerve carefully without injur- 

 ing the femoral vessels. Tie a ligature around the 

 thigh, exclusive of the sciatic nerve. With a large 

 hypodermic needle inject a few drops of curare 

 under the skin of the back. Be sure that the solu- 

 tion does not escape through the incision in the 

 thigh. 



After 'its absorption the curare circulates and 

 is carried to all the tissues except those of the ligated 

 leg. When a complete motor paralysis has been es- 

 tablished in about fifteen to twenty minutes ex- 

 pose both sciatic nerves and place them in loose 

 ligatures. Also expose both gastrocnemii muscles 

 by cutting an oval window in the skin over each. 

 Use weak induction shocks and stimulate the sciatic 

 nerve on the side of the ligature (1) as well as on 

 the normal side (2). In the same way stimulate 

 both gastrocnemii muscles (3 and 4). The follow- 

 ing results will be obtained: (1) positive, (2) nega- 

 tive, (3) positive, (4) positive. 



Annotation. A piece of solid curare (wurare or urare) 

 is pulverized in a mortar and extracted with a solution of 

 0.7 per cent, sodium chlorid until dark in color. Its strength 

 cannot be standardized, but must be determined by the 

 physiologic result. Do not filter, but inject as it is. 



Test the current by applying the electrodes directly 

 to the gastrocnemius muscle. Use a strength of current 

 just sufficient to cause a well-marked contraction. If a 

 strong current is used, the paralysis must be more com- 

 plete, which requires a larger amount of curare. 



Curare paralyzes the motor plates in the muscle, and hence muscle (4) cannot 

 be activated through its nerve, while muscle (3) can be. Both sciatic nerves conduct 

 normally, as can be shown by attaching the poles of a galvanometer to them. In 

 fact, in many instances the stimulation of the nerve on the normal side (4) produces 

 a contraction of the gastrocnemius on the side of the ligature. The elicitation of 



35 



FIG. 13. INDE- 

 PENDENT IRRITABIL- 

 ITY OF MUSCLE. 



A, Dorsal lymph 

 sac into which curare 

 is injected; L, liga- 

 ture upon left thigh. 

 The stimulation of 

 the sciatic nerve at 1 

 is then effective, but is 

 ineffective at 2. The 

 gastrocnemii muscles, 

 when stimulated di- 

 rectly at 3 and 4, 

 give a contraction. 



