1891.] Electromotive Phenomena of the Mammalian Heart. 213 



The latent period of electrical response of auricular and ventricular 

 muscle to direct electrical stimulation is so short that we could not 

 measure it accurately with the means at our disposal. It is certainly 

 less than O'Ol". 



We have sought to measure the rapidity of propagation of the wave 

 in the mammalian ventricle in the same way as Engelmann and 

 Sanderson and Page estimated it in the frog's heart, namely 

 measuring the time interval between the beginning and the culmina- 

 tion of the initial phase. 



In the exposed heart of a dog, breathing warmed air, the rate is 

 generally about 30 mm. in O'Ol", i.e., about 3 metres per second. 

 But the sensitiveness of the form and direction of the variation to 

 slight changes in temperature of different parts of the heart surface 

 must make us hesitate in taking these figures as the correct ones. 



There is a long period of delay in the passage across the auriculo- 

 ventricular groove. A mean of eight observations gave 0'15" as the 

 time elapsed after stimulation of the auricles before the development 

 of negativity at the base of the ventricles. Nearly the whole of this 

 time is taken up in the passage from auricles to ventricles, since it 

 makes very little difference to the time interval, whether the stimuli 

 be applied to an auricular appendage, or the auricles close to the 

 auriculo-ventricular groove. 



Lastly, we have obtained no evidence of the supposed tetanic nature 

 of a cardiac contraction (Fredericq), all our results pointing con- 

 clusively to the contraction being a single wave, starting at the base 

 and passing thence to the apex of the heart. 



The conclusions arrived at by Sanderson and Page in their work 011 

 the heart of the frog and tortoise hold good also for the mammalian 

 heart. 



APPENDIX. 

 On the Electrical Variation of the Heart of Man and the Intact Dog. 



We have also photographed the electrical change of the heart of 

 man and of the dog, with chest unopened, and, in opposition to 

 Waller, we find that the variation is of such a nature as to show 

 negativity always commencing at the base. The greatest effect was 

 obtained by leading off from the apex beat and the right hand, but 

 we found the same character of variation from whatever points 011 the 

 surface of the body we led off, i.e., the electrode nearest the base 

 became negative first. 



The photographs show what the eye could not distinguish clearly, 

 viz., that each beat is accompanied by a triphasic variation, consisting 

 of 1st, a " spike " (basal negativity) ; 2nd, a more prolonged excursion 

 in the opposite direction (apical negativity) ; and 3rd, a large and pro- 

 longed movement in the same direction as the " spike " (basal nega- 



TOL. L. Q 



