iv ELECTROMOTIVE ACTION IN MUSCLE 399 



must not be too small), the current is never reversed by excita- 

 tion, only weakened, or, it may be, totally abolished ; on the 

 other hand, reversal does occur frequently where there is obvious 

 diminution of E.M.F., and is the more marked the greater the 

 fall of potential. The velocity at which the wave of negativity 

 spreads over the heart is reckoned by Engelmann at 2040 mm., 

 but it must be much greater before the heart is excised, and is 

 essentially conditioned by temperature. On exciting the ventricle 

 from the auricle, and in the lead-off from base and apex of the 

 resting ventricle (which produces no current), the base is at first 

 negative, afterwards in most cases positively active to the apex. 

 This is seen in the spontaneously beating heart, as well as in 

 artificial excitation of the auricle. Since the negativity of the 

 base appears first after the auricular contraction has passed by, it 

 cannot be due to excitation of the auricle, which is also seen from 

 the magnitude of the effect, as contrasted with the very small 

 deflection obtained on leading off directly from the auricles. It 

 must, therefore, be assumed that the excitation of the ventricle 

 commences at the base under normal conditions. 



There is a considerable difference between the results of 

 Engelmann and Marchand, and those which Burden- Sanderson 

 and Page (36) obtained from the frog's heart by the same rheo- 

 tome method. They investigated the action current of the ven- 

 tricle when separated from the auricle by a ligature, and excited 

 with single induction shocks by means of a (specially constructed) . 

 rheotome. 



These experiments also showed that each excited point of the 

 heart's muscle loas negative to each point not excited, and that the 

 process of excitation (i.e. negativity) was equally distributed from 

 the seat of excitation on all sides, and that with a considerably 

 greater velocity than Engelmann had calculated. According to 

 the measurements of Burdon-Sanderson and Page the velocity of 

 the wave of negativity in the frog's heart is about 125 mm. per 

 sec. at 1 2 C., while Engelmann only reckons it as 2040 mm. 

 At each point of the ventricle the negativity quickly reaches a 

 certain height, at which it remains for a comparatively long time 

 (more than 1 sec.), and then slowly sinks down again. The total 

 duration of the localised negativity at +18 C. is 1'6 sec., at 

 + 12 C., 2'1 sees, (on an average 0'2 sec. Engelmann). These 

 time-values correspond pretty exactly with the contraction period 



