ELEMENTARY EXPERIMENTAL PHYSIOLOGY 53 



from the cardiac end or from the oesophagus. Fix this to the 

 frog-board by means of a bent pin passed through the lumen. 

 Connect it with a heart lever by a thread and hook (Fig. 59). Make 

 the lever write on a very slow drum. Keep the preparation moist 

 and observe whether any movements are recorded. Pinch the 

 ring with forceps and record the resulting contraction. 



The action of certain drugs may be studied on this preparation. 



Under the microscope examine teased preparations of skeletal, 

 cardiac and visceral muscle fibres and a preparation of the endings 

 of motor nerves in skeletal muscles. 



K. THE PASSAGE OF AN IMPULSE ALONG A NERVE 



(This belongs to Lesson VIII.) 



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 the current may 

 be sent into one or other of the pairs of electrodes (see p. 84). 

 Make a nerve-muscle preparation with the nerve complete to the 

 spinal column, arrange ,the preparation on the frog-board and place 

 the nerve upon the electrodes 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 



FIG. 51. Arrangement for investigating the rate of passage of an impulse 



along a nerve. 



nerve stimulated through each pair of electrodes. Finally, put 

 a time tracing of T J^ of a second on the drum and measure the 

 length of nerve between the two pairs of electrodes (Fig. 51). 



Lesson XI. Apparatus as in last lessons. 



Tetanus Spring. Microscopes with specimens of teased cardiac and visceral 

 muscle. 



