154 GENERAL PROPERTIES OF LIVING TISSUES 



which surrounds the heart. Let one electrode 

 rest on the larynx. Lay upon the tip of the 

 other electrode a strand of lamp wick or absor- 

 bent cotton wet with normal saline solution. 

 Bring this electrode over the heart so that the 

 free end of the strand rests on the ventricle and 

 moves with it. Turn the pole-changer to make 

 this electrode the anode. Make the current. 



At each systole, the portion of the ventricle 

 immediately about the anode will not contract 

 with the rest, but will remain relaxed (local dias- 

 tole). Thus while the greater part of the ven- 

 tricle becomes pale as the blood is squeezed out 

 of its wall by the contraction, the anodal region 

 remains dark red. From this region the relaxa- 

 tion spreads over the rest of the ventricle. Re- 

 verse the pole-changer. Break the current. 



The cardiac electrode is now the cathode. In 

 the systole following the breaking of the current, 

 the cathodal region will remain relaxed during 

 contraction of the ventricle. 



This experiment demonstrates that the galvanic 

 current not only may stimulate, but may check 

 or inhibit contraction. In the former case, the 

 conversion of potential into active energy is set 

 going; in the latter, it is prevented. Inhibi- 

 tion plays a large part in the physiology of the 



