ELEMENTARY EXPERIMENTAL PHYSIOLOGY 51 



The ends of two pieces of ordinary insulated wire are well cleaned 

 and are connected with a Daniell battery ; the clean free ends of the 

 wires are bent back so that there will be smooth surfaces to apply to 

 the heart. The wire connected with the copper of the battery is the 

 anode, that with the zinc is the kathode. 



In the frog's mouth is placed the kathode, for there good contact is 

 obtained with a moist conductor; the anode is placed upon the 

 ventricle. Now it will be found that during the systole of the 

 ventricle that portion of the muscle which is around the anode will 

 be flushed, uncontracted, and bulging outwards the anode at the make 

 of the circuit produces a local diastole during general systole (Fig. 51 A). 

 The rhythmic power of the cardiac muscle around the anode is 

 diminished, so that it remains uncontracted. 



If now the wire be suddenly removed from the heart, the break 

 of the anode causes an increased excitability of the muscle to 

 which it had been applied, there is a local pallor ; the cardiac muscle 

 is here contracted during the general diastole of the heart. The 

 break of the anode produces a local systole during a general diastole. 



The kathode is now applied to the heart and the anode is placed in 

 the frog's mouth. There is produced a local systole during the general 

 diastole of the heart. The kathode increases the excitability of the 

 cardiac muscle, and thus the fibres affected remain contracted. The 

 end of the wire is kept in contact with the ventricle for about a 

 minute and is then suddenly removed ; a flushed and bulging spot will 

 indicate the region to which the wire had been applied. The break of 

 the kathode produces a local diastole during general systole, for the dis- 

 appearance of the condition of katelectrotonus is accompanied by a fall 

 in excitability. 



This simple experiment shows that the make of the kathode and the 

 break of the anode excite, that the make of the anode and the break of 

 the kathode depress. This is also true in the case of nerve. 



CHAPTER XL 

 THE ELECTROMOTIVE PROPERTIES OF MUSCLE AND NERVE. 



IN uninjured and resting muscle and nerve there is no electric current, 

 but during activity a current, the 'current of action,' is produced. 

 Injury causes local activity around the damaged tissue, and is there- 

 fore accompanied by an electric current, the so-called * demarcation or 



