68G PROFESSOR H. N. MARTIN ON THE INFLUENCE OF VARIATION 
The above experiment is remarkable for the very slow pulse observed throughout. 
Even at 37°'5 the pulse was only 173 per minute, whereas in most isolated hearts it is 
over 200 at that temperature. When the temperature was brought down to near 27° 
the extraordinary slow pulse of 18 per minute resulted ; a pulse so slow that although 
each beat was powerful the left ventricle pumped out in each minute less blood than 
was drained off from the aorta by the coronary arteries, so that the level of the 
blood in the aortic exit tube fell lower and lower until the carotid pressure finally 
came down to 41 millims. of mercury. On again heating the blood supplied to the 
heart the organ regained completely its functional activity. Before the cooling 
(observation 13) the pulse rate at the temperature 31°’5 was 85 per minute, and 
pressure in the carotid was 98 millims. of Hg. After the cooling, on again heating, 
we find at the same temperature (observation 46) a pulse of 99 per minute and a 
carotid pressure of 93 millims. of mercury. It is unfortunate that the experiment 
was not continued, but the exceptionally slow pulse obtained was not recognised until 
the tracings were counted out the next day, and as it was the second experiment of 
the same date I was fatigued and stopped so soon as I had satisfied myself that 
reheating the blood had quickened the pulse, instead of going on as usual until the 
heart began to show signs of commencing death. 
Conclusions. 
As regards the question which the preceding experiments were primarily designed 
to answer, their results are decisive. They make it clear that the Mammalian heart 
when quite cut off from all extraneous nervous control, and when supplied with blood 
which has not been altered in composition by products of abnormal tissue change, 
due to abnormal heating or cooling of other organs of the body, does beat quicker 
when warmer blood is supplied to it, and slower when it gets cooler blood. In this 
respect the heart of the Dog behaves quite like that of the Frog. In spite of the 
greater division of physiological duties in the body of the Mammal, and the greater 
subjection of the Mammalian heart to control from special extrinsic nerve centres, the 
Dog’s heart in its own neuro-muscular apparatus is so constituted as to have its rate 
of periodic activity directly controlled by its temperature. To account for the quick 
pulse of fever we need therefore assume no paralysis of extrinsic cardio-inhibitory 
nerve centres and no excitation of cardio-accelerator. The warmed Mammalian heart 
beats quicker because of its own physiological properties. 
In addition to the above main question, several subsidiary points have some light 
thrown upon them. 
(I.) The rate of beat of the Mammalian heart does not directly depend upon the 
temperature of the blood reaching the right auricle, except in so far as this influences 
the temperature of the blood pumped out by the left ventricle and supplied to the 
coronary arteries. It is not the temperature of the blood in its cavities which influences 
