184 GENERAL PROPERTIES OF LIVING TISSUES 



Speed of Nerve Impulse- Smoke a drum, and 

 adjust it for " spinning." Place two pairs of 

 needle electrodes in corks in the moist chamber. 

 Arrange the inductorium for maximal make 

 currents, placing a simple key and the electro- 

 magnetic signal in the primary circuit (Fig. 45). 

 Connect the secondary coil to the side cups of 

 the pole-changer. Connect the end pairs of 

 cups each with one pair of the electrodes in 

 the moist chamber. Make a nerve-muscle prep- 

 aration, preserving the full length of the sciatic 

 nerve. Fasten the femur in the clamp in the 

 moist chamber. Connect the Achilles tendon 

 to the muscle lever. Bring the point of the 

 lever against the drum immediately over the 

 writing point of the electro-magnetic signal. 

 Let the nerve rest on the electrodes, one 

 pair near the end of the nerve, the other 

 near the muscle. Spin the drum slowly. 

 Hold the writing point of a vibrating tuning 

 fork against the smoked paper beneath the 

 line drawn by the signal. Send a maximal 

 induction current through first one pair of elec- 

 trodes and then the other. Determine the inter- 

 val between the moment of stimulation and 

 the beginning of contraction in each instance. 

 [This is done by turning the drum back until 

 the writing point of the signal lies precisely in 



