1878.J 



on Rhythmical Motions of the Heart. 



413 



commencement of the hardening of the ventricle, i.e., 0"'l before the 

 beginning of the prae-contraction. (Sec. I.) The second phase ends 

 about 0" '9 after the beginning of the first, of which the duration is 

 less than a tenth of a second. Consequently the first phase of the 

 variation is completed 0""15 before the commencement of the con- 

 traction of the ventricle, its completion being immediately followed 

 by the beginning of the prae- contraction. The second phase lasts 

 through the period of active contraction. 



9. Time Interval between the Excitation and the Variation. — In the 

 Stannius' heart when the posterior surface of the auricle near the 

 septum is excited, the resulting contraction (as stated in 4) follows 

 the excitation at an interval of about two- thirds of a second. In this 

 case the first phase of the variation precedes the contraction by a very 

 constant interval of a quarter of a second. When the heart is excited 

 from the ventricle half way between the base and apex, left side, the 

 delay is diminished to about a third of a second, but there is no 

 diminution of the interval bet ween the initial phase of the variation 

 and the contraction. 



10. Effect of Injury on the Variation. — If in a normal entire heart, 

 led off at base and at apex, the surface of the ventricle near the base 

 is injured, the character of the variation is changed, the second phase 

 ("apex- negative") being intensified. If the apex is then similarly 

 injured, the second phase is abolished, the variation being indicated by 

 a single large excursion in the direction of the first phase ("apex- 

 positive "). 



In the ventrical preparation, the variation, provided that the surface 

 of the organ be uninjured, exhibits two phases, of which the first 

 is identical with the first phase in the entire heart, the second is 

 represented, when investigated with the aid of the capillary electro- 

 meter, by a larger excursion in the direction "apex-negative," 

 of which the amplitude is not so great as that of the single 

 excursion observed after injury of the apex. After a time the ex- 

 cursion diminishes in extent and duration, so that, finally, the 

 characters of the normal variation reappear. In a similar manner, if 

 now the surface of the ventricle is injured, similar phenomena to those 

 already described, with reference to the entire heart, present them- 

 selves, according to the seat of the injury. If it is at the apex, 

 whether it be mechanical or chemical, the whole variation is repre- 

 sented by a single large excursion (apex-positive) ; if it is at the base 

 there is a pree-excursion, in which the apex becomes momentarily 

 positive, followed by a more prolonged excursion in the opposite direc- 

 tion, corresponding in direction to the second phase. 



It has been already shown, in 6, that the electrical difference be- 

 tween a sound and an injured surface is not materially affected by 

 distance. In like manner, the excursions which present themselves 



