ADVANCED EXPERIMENTAL PHYSIOLOGY 12S 



its distension with blood. There are no blood vessels in a frog's 

 cardiac muscle. 



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 con- 

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

 upon the ventricle. Now it will be found that during the sys- 

 tole 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. 123, 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 disappearance 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 XVI 



THE EFFECT OF A CONSTANT ELECTRICAL CURRENT UPON 

 THE EXCITABILITY AND CONDUCTIVITY OF NERVE 



The passage of a constant current produces changes in the 

 excitability of nerve. At the anode there is a condition known as 

 anelectrotonus, the excitability is diminished ; at the kathode there 

 is an increase in excitability, a state of katelectrotonus. The con- 

 ductivity is also affected, there is a fall in both the anodic and 



