58 EXPERIMENTAL GENERAL PHYSIOLOGY 



be difficult to find it for a muscle-nerve preparation. The finding 

 of a position where there is no response on closing the key is, how- 

 ever, not essential in this experiment. 



(7) Keeping the key closed, slowly rotate the limbs of the rheonon 

 from the minimum position to the maximum position. If the 

 conditions are favorable this can be done without calling forth i 

 response. 



(8) Without opening the key, slowly rotate the limbs back- 

 ward from the maximum to the minimum position. One ma^ 

 thus send through a nerve a strong current and may withdraw the 

 same without causing a contraction of the muscle. Keep the ke^ 

 closed. 



(9) Quickly rotate the limbs from minimum to maximum; th( 

 muscle responds. Quickly rotate from maximum to minimum; th( 

 mus<*le responds. 



From the preceding observations one may conclude that respons( 

 to electric stimulation is elicited not by the simple flow of an elec- 

 tric current through the irritable tissues, but by a more or lesi 

 sudden change in the strength of the current. The opening anc 

 closing of a galvanic current, also its sudden increase or decrease 

 serves as an efficient stimulus, while the gradual increase or decreast 

 in the strength of the current causes no response. 



XV. TO DETERMINE THE INFLUENCE OF CATHODE AND 

 ANODE POLES. 



Many of the phenomena of muscle-nerve physiology were inex- 

 plicable until a difference was noted (von Bezold, 1860) in th( 

 influence of the anode and cathode. This difference in the influ- 

 ence of the two poles may be best observed by use of the sartorim 

 muscle of a frog. 



1. Appliances. A double myograph and support ; recording drum 

 Daniell cell; Pohl commutator; Du Bois-Reymond key; non-polar- 

 izable electrodes; five wires; electrode clamp and support. 



2. Preparation, (a) Set Up a Pair of Non-polarizable Electrodes 

 (See Appendix, 9.) 



(b) A Double Myograph. A most efficient as well as convenient 

 and economical double myograph may be arranged for this experi- 

 ment as indicated in Fig. 35. 



Two common muscle levers, as shown in the figure, are used, 

 These are held in position by common clamps and heavy support 

 The upper myograph must be reversed and its lever counterpoised 

 by elastic bands. Between the two myographs a small wooden 

 block, with a longitudinal hole for the loop of thread which holds 

 the muscle, is held by a clamp. 



