192 EXPERIMENTAL PHYSIOLOGY. 



6. Action Current of Muscle. 



(a.) Use the same muscle preparation, or isolate the 

 gastrocnemius with the sciatic nerve attached. Divide the 

 muscle transversely, and lay the artificial transverse section 

 on one electrode, and the longitudinal surface on the other. 

 Observe the extent of the deflection. 



(b.) Adjust a du Bois induction apparatus for interrupted 

 shocks, placing it at some distance from the galvano- 

 meter. 



(c.) Take the demarcation current, observing the deflection, 

 and allow the spot of light to take up its new position on 

 the scale. Stimulate the muscle by the ordinary electrodes 

 to throw it into tetanus, and observe that the spot of light 

 travels towards zero. This was formerly called the " negative 

 variation of the muscle current." It is now called the " action 

 current " of muscle. If the gastrocnemius be used, stimulate 

 the sciatic nerve. Care must be taken that the muscle does 

 not shift its position on the electrodes. 



LESSON XXXIX. 



DEMARCATION AND ACTION CURRENT IN 



NERVE-ELECTRO-MOTIVE PHENOMENA 



OF THE HEART CAPILLARY 



ELECTROMETER. 



1. Demarcation Current of Nerve. 



(a.) Render the galvanometer as sensitive as possible by 

 adjusting at a suitable height the north pole of the magnet 

 over the north pole of the upper needle. 



(b.) Prepare N.P. electrodes for a nerve. In this case, 



