OF TEMPERATURE UPON THE BEAT OF THE DOG’S HEART. 
675 
sometimes increased 80 per cent. An increase of 80 per cent, above the average will 
more than account for the quickest pulse observed by me at normal temperatures. 
Second, it will be seen that, quite independent of any changes of temperature, the 
heart beats slower towards the end of an experiment than it did at the beginning, 
although its action may still be regular and each pulsation powerful. This is 
undoubtedly due to altered nutrition resulting from the use of Calf’s blood, as it was 
not observed, or at least not until much later in my earlier experiments (2), when Dog’s 
blood was employed. In consequence of this gradual and progressive slowing of the 
pulse it might be objected in a cooling experiment that any observed diminution of the 
rate of heart-beat was dependent on other conditions than cooling of the organ. To 
meet this objection, inmost instances after a series of cooling observations a series of 
heating has been made on the same heart, and these show that in every case the heart 
beats much quicker when again warmed. This makes it clear that the slow pulse 
previously observed was not due merely to progressive malnutrition of the isolated 
heart, but was mainly dependent on the lower temperature to which the organ was 
exposed. Taking for exampde Experiment L, we find that at l h 34™ p.m. the heart 
beat 246 times a minute at the temperature of 37°‘S C. Forty-three minutes later 
(at 2 h l7 m p.m.) it beat only 217 times per minute at the temperature 38°T C; 
but meantime the pulse-rate, at l h 57 m M.P., had been down to 73 per minute, the 
temperature being 27°'8 C. This slow jmlse being followed twenty minutes later 
by one nearly three times as fast cannot of course have been conditioned by any 
progressive diminution of functional capacity dependent on the prolonged use of Calf’s 
blood ; this becomes still more obvious when, later on in the same experiment, we find 
a second cooling accompanied by a slower pulse, and a second heating by a quicker. 
Third, it may be noted that in no case does any one of the experiments given last 
longer than two hours, and that, with one exception (Experiment VI.), it is stated 
1 that the observations had ceased because of some obvious abnormality in the heart’s 
I action. In my earlier experiments with isolated hearts a practically normal beat 
often lasted for four hours or longer. They were however carried out on a different 
plan, which allowed of the use of defibrinated Dog’s blood to nourish the heart. 
Instead of permitting the left ventricle to pump blood out through a wide aortic 
cannula, the only exit left was through a narrow cannula in one carotid, and, in 
correspondence with this fact, the tube supplying the superior cava was also narrow. 
In the present series of experiments the widest possible cannulse' was placed in the 
aorta and vena cava, and all the tubing attached to these, and the stopcocks upon it, 
had a bore as wide as that of the cannulse. Under such circumstances the heart pumps 
round three or four litres of blood in a very few minutes, and with a smaller amount 
the stopcocks and clamps used to make the flasks C and D alternately feeding and 
recipient, would have to be changed at such short intervals as to make it impossible 
to carry on any uniform series of consecutive observations. With the original method 
1000 to 1500 cubic centims. of whipped blood was enough for convenient use, and 
