ELECTROMOTIVE PHENOMENA OF THE HEART. 447 



uninjured ventricle, with the leading-off electrodes at a similar distance 

 apart. According to Engelmann's curve (Fig. 1 in his paper), the relation 

 between the differences observed and the time elapsed after excitation 

 was as follows : — 



No deflection. 

 Beginning of variation. 

 Negative maximum. 

 Equipotentiality. 

 Positive maximum. 

 End of variation. 



No. 6 shows the appearance that such a curve would represent if 

 reduced to the same scale as No. 5. 



The rate of propagation of the electrical response, which is the 

 sign of the excitatory state, admits of being determined by two methods. 

 The first is founded on the comparison of two measurements, i.e., of the 

 time after excitation at which the first indication of electrical changes are 

 appreciable at the proximal contact, and of the distance of that contact 

 from the seat of excitation. This method was used by Engelmann, and 

 led in his hands to the conclusion that the rate of propagation is less 

 than 50 mm. per second. We were, however, able to show in 1882, 

 that correct observations cannot be obtained by a single comparison of 

 the distance between the seat of excitation and any point in its progress, 

 with the time at which its arrival at that point is indicated, because 

 neither the exact starting-point of the excitation wave, nor the moment 

 at which it starts, can be determined with certainty. This being so, the 

 only satisfactory way of measuring the rate of transmission by this 

 method is to compare the results of two observations, in each of which 

 the wave of excitation starts from the same point, but in the one, the 

 proximal electrode rests on a spot nearer to the starting-point than 

 in the other. The relation between the difference of time at which each 

 of the two points is attained and their distance from each other, 

 accurately represents the rate of propagation. An equally correct 

 method on the same principle is to compare two observations in which, 

 the position of the proximal electrode being unchanged, the exciting 

 electrodes are at varying distances from it. It was thus determined 

 that at 12° C. the rate of propagation might be as much as 125 mm. per 

 second, but only so long as the ventricle was perfectly fresh (cf. p. 443). 



The second method, which consists in measuring the time-interval 

 between the beginning and culmination of the first phase, yields similar 

 results, but it has not been much used. There is, however, no reason 

 to doubt that it is equally reliable. 



Electromotive phenomena of the mammalian heart — In 1892, 

 Bayliss and Starling x investigated the electrical phenomena of the 

 normal beat in the mammalian heart with maintenance of circulation. 

 Their experiments showed that in the ventricle of the dog, when the 

 leading-off electrodes to the electrometer are applied to the base and 

 apex respectively, the excursions of the mercurial column are such as 

 to indicate that " the variation is always diphasic, . . . negativity of the 

 base preceding that at the apex," whether the pericardium be opened 

 or not. They found that difference of temperature and differences of 

 physiological state between the two contacts produce modifications 

 1 Interned. Monatschr. f. Anat. u. Physiol., Leipzig, 1892, Bd. ix. Het't 7. 



