Electromotive Phenom. of the Mammal. Heart. 271 



tlie electrical change, we attempted to use the repeating rheotome 

 both with galvanometer and electrometer; hut found it impossible, 

 owing to the fact that the effect of each stimulus is not always pre- 

 cisely equal to that of the one preceding it, so that the movements 

 of the galvanometer-needle and of the meniscus of the electrometer 

 were too irregular to afford any information whatever. 



Latent period of ventricular and auricular muscle. 

 This was found to be so short, in cases of direct excitation, that 

 we could not measure it. The light used (lime-light) was not power- 

 ful enough to enable us to give a sufficiently rapid rate of movement 

 to our photographic plates; we could, in fact, obtain no image when 

 our rate of movement exceeded 10 centim. per second. The latent 

 period of the electrical change is certainly not more than .005". 



Velocity of propagation from auricle to ventricle. 

 If we led off the base and apex of the ventricle and excited 

 some point of the auricle, we found that a considerable period of time 

 (.12" to .16") elapses before there is any electrical variation in the 

 ventricle. This delay occurs chiefly in the passage of the wave 

 from auricle to ventricle, for we found that it made very little 

 difference in the time required, whether we excited the auricles at the 

 tip of an appendage or close to the auriculo-ventricular groove, or 

 again, whether we led off from two points near the base or from 

 two points near the apex of the ventricle. Thus, in one experiment, 

 when the tip of the right auricular appendage was excited, the time 

 that elapsed before the electrical change occurred at the base of the 

 ventricle was .14"; the auricle was then excited, close to the auriculo- 

 ventricular groove and the time of propagation was now .13". The 

 numbers obtained in various experiments were the following. 



a) Exciting appendages and leading off base and apex: 

 0.13", 0.12", 0.14", 0.13", 0.13", 0.12". 



b) Exciting auricle near groove: 

 0.13", 0.14", 0.16". 



The last number was obtained when exciting the middle of the 

 posterior surface of the auricles. 



