Electromotive Phenoui. of the Mammal. Heart. 269 



the curve was dipliasic, indicating negativity of the point nearest the 

 excited place preceding negativity of the further electrode, yet when the 

 excited part was cooled, a diphasic curve of the opposite nature was 

 produced, indicating negativity of the points further from the excited 

 point pi'eceding negativity of the point nearer; moreover, it appeared 

 to the eye as if the further half contracted before the nearei- (cooled) 

 half. Unfortunately, through lack of material we were unable to re- 

 peat this experiment, and would not lay too much stress upon it. 

 (Plate XVI. figs. 14, 15, 16.) 



n. Time measurements. 



In attempting to make accurate time measurements of the latent 

 period of contraction of the heart muscle, or of the velocity of propa- 

 gation of the wave of contraction in warm-blooded animals, difficulties 

 are met with which do not occur in working on cold-blooded animals. 

 We cannot take the heart out of the body, or interrupt its blood- 

 supply without its losing at once its normal excitability and soon dying 

 altogether. We cannot use the Stannius ligature to bring it to a 

 standstill, and although we can stop the heart by exciting the vagus, 

 yet the duration of the stoppage must be extremely short, or the blood 

 becomes deoxygenated and affects the heart injuriously; moreover, 

 under vagus excitation the conditions of the ventricular walls as re- 

 gards tension, are abnormal — the heart becoming enormously distended. 

 Again, excitation of the vagus causes a marked change in the excita- 

 bility of both auricles and ventricles, in the case of propagation from 

 auricle to ventricle and probably from one part of the muscular wall 

 to another; as a rule, in fact, we found the auricles inexcitable to 

 artificial stimulation under vagus inhibition. 



We therefore made use of a method suggested by Prof. Gotch. 

 If any part of the auricle or ventricle be stimulated at a rate slightly 

 above the normal rhythm, the heart will beat regularly in response 

 to each stimulus, and not only will the ventricle follow the auricle, 

 but if the ventricle itself be excited, the auricle will beat in regular 



