26 



Note the relationship of the second contraction to the first, 

 upon which it is superimposed. Mark the moments of stimu- 

 lation, and take a time trace. 



2. Now disconnect the drum from the primary circuit and 

 introduce a spring, so that as it vibrates it makes and breaks 

 the current by dipping into a mercury cup (see fig. 13). 

 Adjust the current to stimulate on breaking. (1) Set the 

 drum going slowly, and set the spring so that it makes and 

 breaks 3 to 5 times per second (timing with your watch). 

 and note its length. Bring the point of the lever upon the 

 drum. Start the spring vibrating. Open the key in the 

 secondary circuit and take a trace for about 3 or 4 seconds, 

 then close the key, but let the drum run till the lever falls to 

 its previous level. 



(2) Now move the lever to another part of the drum, shorten 

 the spring, and take another trace of the same duration. 



(3) Repeat several times, shortening the spring, and each 

 time noting the length of the spring. 



(4) Finally connect up the Neef 's hammer of the induction 

 coil a very short rapidly- vibrating spring and take another 

 tracing. Take a time trace of intervals of TO sec. by means 

 of an electromagnetic marker. Fix the tracings and study 

 the results of a succession of stimuli, and formulate your 

 CONCLUSIONS from these results. 



IV. THE NERVOUS MECHANISM. 



I. Simple Neuron Action, 

 i. How is the Activity of the Neuron manifested ? 



METHODS. 1. Make a nerve-muscle preparation, leaving 

 the foot attached as a signal as on p. 19, (1) to (6), dissecting 

 out the whole length of the sciatic nerve to the spinal cord, 

 and taking care to leave attached to the nerve a long piece o/ 

 the branch to the posterior muscles of the thigh. Stimulate the 

 sciatic nerve, using an induction coil and Neef's hammer. 

 There is no manifest change in the nerve, but there is a change 



