220 
DR. A. D. WALLER AND MR. E. W. REID ON THE 
Tracing 5. 
Contractions of the excised Rabbit’s 
heart from the 6th to the 75th 
minute after excision ; showing 
increasing prolongation of the 
ventricular contraction. 
The two points to which we specially directed 
our attention at this stage were the changes in the 
duration of the ventricular contraction, both spon¬ 
taneous and excited, and in the leno-th of the latent 
period of stimulation. With regard to previous 
observations, we know of none, with the exception 
of a very imperfect datum consigned in Landois’ 
“ Physiologie,” 1880, p. 95, where he gives the 
maximum duration of the systole of the excised 
Rabbit’s heart as '48 second, the normal duration 
being '25. Of the period of latent stimulation we 
have nowhere found auv mention.* 
«/ 
§ III. Du ration of systole in the excised heart. 
Our observations show that from the moment of 
excision the ventricular contractions steadily increase 
in duration to a maximum of about 6 seconds, the 
normal duration being about ‘3 second. This state¬ 
ment holds good for hearts of Cats, Dogs, and 
Rabbits removed and observed at ordinary room- 
temperature (16° Cent.). The hearts of these 
animals at 16° Cent, give contractions far exceeding 
in duration that of the contraction of the Frog’s or 
Tortoise’s heart at the same temperature. Table A 
and Tracing 5 are illustrative of this statement. 
The chief cause of this change is an alteration of 
temperature, the heart in situ being at a tempera¬ 
ture of 37° to 40°, while the temperature of the 
room was between 15° and 18°, or during the winter 
as low as 12°. That the temperature factor was 
* Three times in the course of our observations we noticed 
that immediately after decapitation the diaphragm on the left 
side contracted simultaneously with the beat of heart. In one 
case the contractions of the diaphragm were so strong as to 
bend the body of the animal to the left side with each beat of 
the heart. We supposed that the phenomenon was one of 
secondary conti'action, the left phrenic being excited by the 
electromotive change of the heart at each contraction. The 
contractions of the diaphragm were at once arrested by section 
of the phrenic below the heart. 
