60 EXPERIMENTAL GENERAL PHYSIOLOGY 



The electric apparatus should be set up as shown in Fig. 36. 



With this arrangement either electrode may be made the anode, 

 the experimenter needing 'only to reverse the commutator bridge to 

 reverse the position of the anode and cathode. 



The recording drum or kymograph should rotate rapidly. The 

 recording points of the myograph levers should be adjusted so that 

 the point of the upper one touches the drum vertically over the 

 point of the lower one. Adjust the marker Cr so that it will indicate 

 the time making and breaking the circuit i. e., so that it will record 

 on the drum the time of making stimulus and the time of breaking 

 stimulus. The recording point of the time marker should, of course, 

 be in the same vertical line with the myograph points. The moist 

 tips of the N. P. electrodes should be so adjusted as to touch the 

 muscle above and below the loop of thread. 



FIG. 36 . 



(1) Close the key. If the preparation has been successful the 

 half of the muscle in contact with the cathode pole will respond 

 before the other one. 



(2) Break the current. The anode will respond first. 



(3) Reverse the direction of the current and repeat (1) and (2). 



(4) Vary the strength of the current through use of the simple 

 rheocord and determine whether the results are the same for currents 

 of different strength '. 



Law I. The make contraction starts at the cathode and the break 

 contraction starts at the anode. 



When irritable tissue, muscle or nerve, is subjected to a galvanic 

 current the response to the stimulation begins in the region of the 

 cathode on making the current, and in the region of the anode on 

 breaking the current. 



Would the foregoing observations justify the following statements ? 



(1) Cathodic contractions, or make contractions, may be caused 

 by a galvanic current which is too weak to cause anodic contractions, 

 or break contractions. 



(2) Cathodic contractions, or make contractions, are stronger than 

 anodic contractions, or break contractions. 



Law II. With a given strength of current the influence of the cathode 

 pole is more irritating than the influence of the anode. 



