ELECTRO-PHYSIOLOGY 



731 



then quickly, until (i) follows again (Gotch). The time between 

 the beginning and the top of rise (i) is believed to correspond to 

 the time of transmission of the active state from the base to the 

 apex. The rate of propagation on the rabbit's ventricle varies 

 from i to 3 metres a second, according to the rate of the heart- 

 beat. The fourth phase is due to the fact that the effect in the 

 neighbourhood of the aorta (and pulmonary artery) is more 

 transient than the apex effect. By altering the position of the 

 contacts the record can be made diphasic, or even triphasic. 



In the ventricle of the frog and tortoise the same order of 

 development of the negative change is seen, the base first 

 becoming relatively negative, then the apex, and then the 

 neighbourhood of the origin of the aorta (Fig. 281). 



FIG. 281. ELECTROMETER RECORD FROM TORTOISE HEART (GOTCH). 



One contact upon the sinus, the other on the apex of the ventricle. One 

 complete beat shown. Upward movement signifies relative negativity of the sinus 

 contact. The dark line A shows the auricular effect, and the dark line V the 

 ventricular effect. Time-trace at top, one-fifth seconds. 



Under certain conditions the action current of the heart may 

 stimulate the phrenic nerves, causing the diaphragm to contract 

 synchronously with the heart. 



The Human Electro-cardiogram. An electrical change accom- 

 panies each beat of the human heart. Waller first showed how 

 this may be demonstrated by means cf ths capillary electrometer. 



Einthoven and Lint then investigated the phenomenon on a 

 large number of persons. From the photographic records of the 

 movements of the meniscus (Fig. 282) they constructed the true 



