end cut off. Non-polarizable electrodes are placed one on the 

 ////injured surface, near one end, and the other on the ////injured sur- 

 face, near the other end, and led off to the capillary electrometer. 

 A deflection may he noted on opening the short circuiting key, indi- 

 cating differences in the electrodes. Note its direction and amount. 

 Now one cf the non-polarizable electrodes is placed on the injured 

 end, the other is left near the uninjured end of the muscle. Again 

 note the deflection of the galvanometer. Is it greater than before? 

 In which direction does it indicate that a current is flowing? 



233. Measurement of current of injury. Connect injured and 

 uninjured surfaces of a cut sartorius, with an electrometer in cir- 

 cuit, to the slider and O-post of a rheocord. Connect a dry cell 

 through a key to the O and lo-meter post of the rheocord. Either 

 both negative or both positive poles of muscle and cell must be con- 

 nected to the O-post. (See fig. in Harvard Apparatus Company 

 Catalogue, p. 22. ) Move the slider to a position where no current 

 flows through the galvanometer when the cross circuiting key is 

 opened. The fractional voltage of the dry cell (1.4 volts) can then 

 be read directly from the rheocord and will just balance the voltage 

 of the muscle. Result ? 



234. Current of action. Stimulate the muscle by pinching while 

 a current of injury is flowing. How is the electrometer affected? 

 Do you see now why the action current was called the "negative 

 variation'' of the current of rest? 



235. The bio-electric currents are stront/ enouyh to stimulate 

 nerre. The "Rheoscopic Fro;/ Preparation". 



a. Make two nerve-muscle preparations, A and B. Lay the 

 nerve cf A lengthwise over the muscle of B. Stimulate B through 

 its nerve. Does the muscle of A contract as well as that of B ? 



1). Cut the B muscle near its tendon end. Lay nerve of A care- 

 fully on muscle of B, touching injured and uninjured surfaces. Is 

 there any contraction? Now r stimulate the nerve of B. Does the 

 A muscle also contract? How do you interpret each of the results 

 obtained in the above experiments? 



c. Lay the nerve of A lengthwise across the beating heart of the 

 frog. The heart is left in the body of the frog but exposed by 

 cutting away the pectoral girdle and pericardium. \Yhat happens ? 

 Explain. This experiment succeeds best if the frog furnishing the 

 nerve muscle preparation is previously kept on ice for some time. 



236. Polarization current. Connect two keys (A and 15) in 

 circuit with two dry cells. Connect a frog's muscle, by means of 



69 



