MUSCLE AND NERVE 



57 



following procedure may be tried : Connect a rubber ball by means of 

 rubber tubing with a recording tambour, and request the subject to 

 hold the ball between his middle finger and thumb. Adjust an electro- 

 magnetic signal underneath the tambour in such a way that their 

 writing points come to lie in the same ordinate. Place a tuning-fork 

 fastened to a separate stand below the latter, its pointer being directed 

 against the rotation of the drum. The binding-posts of the signal are 

 then connected in series with a key, posts 1 and 2 of the fnductorium, 

 and a dry cell. From the secondary coil two wires are led off to a pair 

 of clinical electrodes. The large indifferent electrode is placed upon the 

 outer aspect of the arm of the subject, whereas the pointed one is held 

 against the region of the median nerve at the bend of the elbow. 



Allow the tuning-fork to vibrate. Spin the drum with your left 

 hand, and close the key with your right hand. The moment of 

 stimulation will be recorded by the signal, and the moment of con- 

 traction of the flexor muscles by the tambour. Draw ordinates and 



FIG. 36. CONDUCTION IN BOTH DIRECTIONS IN GRACILIS MUSCLE. 



A and B, Segments of gracilis muscle divided by cut (C); S, point of stimulation; N, 



motor nerve and its branches. 



determine the length of the latent period. Repeat this experiment 

 while the stimulating electrode is held over the brachial nerves above 

 the clavicle. Again determine the length of the latent period. The 

 difference in the latency between the two contractions corresponds to 

 the time consumed by the impulse in its passage from the region of 

 the clavicle to the elbow. Measure this distance, and calculate from 

 these data the rate of transmission of the nerye impulse. 



4. Nerve-fibers may be Made to Conduct in Both Directions. 

 Pith a frog and reflect the skin from the ventral surface of the thigh. 

 Cut transversely across t|ie sartorius muscle near the knee and again 

 near the ilium. Isolate the muscle along its outer border and turn its 

 entire mass inward, so that its under surface is brought into full view. 

 Its nerve will be seen to enter near the middle of its inner border, where 

 it divides, sending branches toward both poles of the muscle. With 

 the scissors cut transversely across the different muscle-fibers well into 

 the triangle formed by the dividing nerve, so as to destroy the con- 



