27 



in the muscle to which the nerve goes. (Keep the preparation 

 cool and moist.) 



2. Pinch your ulnar nerve behind the internal condyle of 

 the humerus a sensation is produced. 



Where is the change manifested ? 



ii. Does the Impulse travel in one or in both Directions ? 

 (Paradoxical Contraction.) 



METHOD. In the preparation just made, isolate the branch 

 of the nerve to the posterior muscles of the thigh and place 

 it upon the electrodes. Stimulate, and note whether the 

 gastrocnemius contracts. 



What is the explanation of this ? 



iii. The Excitation of the Nerve may be measured by the 

 Extent of Contraction of the Muscle to which it goes. 



Study the records of the experiments, p. 21, I., on the 

 influence of Strength of Stimulus. 



iv. Is a Neuron stimulated throughout its whole Extent at 

 , once, or does the Change pass along it ? 



METHOD. Place a commutator with the cross wires removed 

 in the secondary circuit of an induction coil, and connect 

 a pair of pin electrodes with each pair of the terminals, so 

 that, by moving the bridge, the current may be sent into 

 one or other of the pairs of electrodes. Connect the muscle 

 of the preparation with a crank lever (p. 21), and place 

 the electrodes upon the nerve one pair near to and one 

 pair as far as possible from the muscle. Bring the lever 

 against a very fast drum, and take a separate tracing of the 

 muscle twitch with the nerve stimulated through each pair of 

 electrodes. Finally, put a time tracing of y^o of a second 

 on the drum and measure the length of nerve between the two 

 electrodes. 



Calculate the rate of passage in metres per second. 



II. Reflex Action. 

 1. Phenomena of Reflex Action. 



METHOD. 1. Arrange an induction coil with Neef 's hammer. 

 Have a basin of water beside you. 2. Decapitate a frog, but 



