492 APPENDIX 



(use the glass rod), muscle No. 1 will be stimulated to contraction by 

 the action-current passing over muscle No. 2. 



B. In the Heart. Open the thorax of the frog from which the two- 

 nerve-muscle preparations were taken sufficiently to expose the still 

 beating heart. With the glass rod arrange the nerve of a gastrocnemius 

 longitudinally over the heart. The former muscle should contract at 

 each heart-beat. If it does not, snip off the central end of the nerve, 

 place it on the heart's apex and loop the nerve over so that it touches the 

 base of the heart; or even slightly injure the heart-apex mechanically. 



It is demonstrated by these experiments merely that when a muscle 

 contracts under experimental conditions an appreciable current passes 

 over it, or at least that a difference of potential is developed in different 

 parts of the muscle. Application of a delicate galvanometer proves 

 this current to be electrical. It may be easily shown that it precedes the 

 contraction of the muscle (see Expt. 69), and that in case of stimulation 

 through a nerve the current starts at its entrance-place and passes over 

 the muscle. (In these respects the contraction-wave is similar.) When 

 one end of a muscle is injured so as to contract less normally, the con- 

 tracting end is electronegative to the part less active. In an active 

 whole muscle points near its equator are electro-negative to points 

 farther away. The rate of the action-current in frog's muscle (and nerve) 

 is about 3 meters per second, its average duration being about 0.004 

 second, while its strength in a frog's gastrocnemius is about 0.08 volt. 

 Whether an electrical current accompanies the contraction-wave just as 

 this action-current precedes it is still in dispute. Some find evidence 

 that this electrical condition lasts as long as does the shortening of the 

 muscle. 



Expt. 51. Electricity Developed in Necrobiosis. (Current of injury, 

 demarcation-current.) (Apparatus: Capillary electrometer, normal 

 saline clay, glass rod, nerve-muscle preparations, skin, stomach.) 



(A) Prepare the gastrocnemius muscle and its nerve with great care, 

 gentleness, and speed. Even with a capillary electrometer no elec- 

 tricity can be found in the muscle when its ends are connected by a con- 

 ductor (except when the muscle contracts, and that is its action-current). 

 Cut off the lower third of the muscle and bring the end of the sciatic 

 against the cut end. The remainder of the muscle contracts. Apply 

 the electrometer and a vigorous current will be found in the muscle 

 passing from the injured end upward; the injured surface is electro- 

 negative to the uninjured lateral surface. (B) Try the inside and out- 

 side of the frog's skin and the inside and outside of its stomach. The 

 outside is electro-positive to the inside in both cases. (C) Roll a small 

 bit of the saline clay into a pencil 3 cm. long and i cm. in diameter and 

 bend it in the shape of U on the dried dissecting-plate. Make a gastroc- 

 nemius nerve-muscle preparation. Place the nerve near its muscle on 

 one arm of the clay; lift the other part of the nerve with the glass rod and 

 drop the freshly cut end on the other arm of the clay. The muscle will 

 twitch, stimulated by the demarcation-current from the nerve. 



