ELECTRO-PHYSIOLOGY 



645 



that of the rest of the heart. If the tissue is injured at either leading- 

 off electrode, the corresponding phase of course disappears. 



In the uninjured mammalian heart, beating as far as possible 

 under normal conditions, the sequence is the same, the diphasic 

 variation showing first base negative to apex, then apex negative to 

 base. Statements to the contrary seem to have been founded on 

 observation of injured hearts, or hearts placed under abnormal 

 conditions. For example, when the base of the heart is cooled, the 

 variation first becomes triphasic, the sequence of the relative nega- 

 tivity being base apex base; and finally diphasic with a sequence 

 the reverse of the normal, the apex being first negative, then the 

 base. 



The Human Electro-cardiogram. An electrical change accom- 

 panies every beat of the 

 human heart. Waller has 

 shown how this may be 

 demonstrated by means of 

 the capillary electrometer. 

 His experiments and later 

 work by Bayliss and Star- 

 ling indicate a triphasic 

 variation first base nega- 

 tive to apex, then apex 

 negative to base, and then 

 again base negative to 

 apex. 



Einthoven and Lint have 

 recently investigated the 

 phenomenon on a large 

 number of persons. From 

 the photographic records 

 of the movements of the 



FIG. 



213. ELECTRO CARDIOGRAMS 

 MAN (EINTHOVEN and LINT). 



FROM 



The image of the capillary magnified eight 

 hundred times was projected on a moving photo- 

 graphic plate. The figure is a reproduction of the 

 record (reduced to two-thirds of its original size) 

 obtained from the same individual at rest (upper 



meniscus (Fig. 213) they curve )- and immediately after vigorous muscular 



have constructed the true 



electro -cardiographic are shown below the cardiograms. The sulphuric 



exercise (lower curve). The movements of a tuning- 

 fork, making fifty complete vibrations a second, 



curves* (Fig. 214), which 

 express the actual changes 



acid pole of the electrometer was connected with 

 the thoracic wall in the neighbourhood of the apex 

 of the heart and the mercury with the right arm. 



in the potential difference The elevations A, C, and D indicate negativity of 



between the two points 



base to apex ; the notches B and C, negativity of 



apex to base. 



led off. They distinguish 

 in every one of these constructed electro-cardiograms five points or 

 cusps, three of which indicate negativity of the base of the heart to 

 the apex, and two negativity of the apex to the base. The electro- 

 cardiograms are distinctly affected by exercise and by the position of 

 the body, and may be useful in the investigation of disease. These 

 observers confirm Waller's statement that it is best to connect one 

 electrode with the thoracic wall over the apex of the heart, and the 



* In all accurate work with the capillary electrometer such curves 

 must be obtained by construction from the direct photographic records, 

 which do not themselves give an absolutely true picture of the variations. 



