ELECTRICAL CHANGES IN TISSUES 655 



mammalian heart. When electrodes were placed on the base and apex of the 

 ventricle, in as normal a condition as we could maintain it, we found that the 

 electrical change was of a simple diphasic character, indicating that the wave 

 started at the base and was propagated to the apex, as shown in Fig. 209 (curve a). 

 When, however, the phenomenon was investigated without opening the chest, as 

 can be done by leading off from the right arm and left leg, there was found to be 

 a third phase present, in the same direction as the first. The explanation which 

 we gave was that the excitation process lasts longer at the base than at the apex, 

 so that the electrical negativity at the apex has disappeared before that at the 

 base has completed its time course. The subject was taken up by Einthoven, who 

 invented the string galvanometer (1901, 1903, and 1904) for the purpose of the 

 work. Fig. 210 shows the human "electro-cardiogram," with the designations of 

 the components used by Einthoven (1913). It has been clearly shown that the 

 first wave, P, is due to the auricular contraction, the second phase of the auricular 

 contraction is usually concealed by the commencement of the first ventricular 

 phase, R. The meaning of the small change, Q, is rather doubtful; it is not 

 always present, and appears to belong to the ventricular "complex," as it is called. 

 If so, it may mean that the ventricular excitation wave starts from a point a little 

 distant from the base, or it may be merely a branch current, as it is so minute. 

 The ventricular complex consists of the three deflections, R, s, and T. The first 



FIG. 211. EFFECT OF LOCAL WARMING ON THE ELECTRICAL CHANGE IN THE 

 FROG'S VENTRICLE. 



The first and last parts of the tracing show the normal diphasic effect before and after warming the apex. 

 The second and third parts show the effect of shortening the duration of the excitatory process at the 

 apex by raising the temperature. The relatively greater duration of the process at the base causes the 

 appearance of the third phase, corresponding to Einthoven's T wave. The way in which this happens 

 is shown in Fig. 212. 



(Mines, 1913, 3, p. 200.) 



two obviously represent the commencement of the wave at, or near, the base and 

 its progress to, and arrival at, the apex. But why is it cut short so quickly and 

 followed by the third phase, which indicates excitation at the base 1 It is clear 

 that the equipotential interval between s and T must mean that the whole 

 ventricle is in a state of excitation ; in fact, it corresponds to that part of the 

 mechanical curve of the heart beat in which the entire ventricle is in a state of 

 contraction. In further analysis, there are some facts to which Mines (1913, 3) 

 calls attention, in a paper which contains an admirable account of the electro- 

 cardiogram. There is no reason to suppose that the t wave . is of any different 

 nature from that of the other parts of the complex. It is the end of the total 

 change, as shown by comparison with the monophasic change obtained when the one 

 electrode is on an injured spot. As mentioned above, Bayliss and Starling (1892, 1) 

 pointed out that it must be due to the electrical change at the base lasting 

 longer than at the apex. It is in the same direction as the initial effect, R. This 

 conclusion is confirmed by Mines (1913, 3, p. 201) in experiments in which, by 

 warming the apex of the frog's ventricle, when it was giving a diphasic change, he 

 caused the effect at the latter to take on a more rapid time course, and thus made 

 the base negativity to last relatively longer. Fig. 211 shows that a curve 

 similar to that of the human electro-cardiogram is obtained. But why, in the 

 normal heart, should the base, which is excited first, apparently remain excited 

 last 1 ? Gotch (1910) thought that it was due to the wave leaving the base, passing 

 to the apex, and then back again to the base at the origin of the aorta. He 

 brought it into relation with the development of the heart from a folded tube in 

 the embryo. Meek and Eyster (1912) and Mines (1913, 3) have shown, however, 



