ON THE HEART OE THE DOG. 
147 
justified, we think, in claiming that our results, at least as far as the Dog is concerned, 
come nearer to the truth than do those of Volkmann or of Vierordt. 
Any inference from the results obtained for the Dogf to the heart of Man will 
in the present condition of our knowledge be more or less uncertain. Yierordt 
concludes, though upon no very firm grounds, that the weight of blood sent out 
from the ventricle at each systole in different animals is nearly proportional to 
the body weight. Volkmann also takes the same ratio as holding good for 
different Mammals. 
If the ratio found by us for the Dog can be applied directly to Man it will support 
the results of Fick’s experiments. 
There is one fact, however, which it seems to us makes such an inference 
inadmissible, and that is the difference in pulse-rate between the heart of the Dog and 
the heart of Man : the average pulse-rate for Man is about 72 per minute, the 
average pulse-rate for the Dog about 120 per minute. Ought not this to make 
a difference in the amount of blood thrown out at each systole \ 
If the supposition is true that the ventricle in the Dog, and presumably in Man 
also, is distended during each diastole to about its maximum capacity, it would 
seem that variations in pulse-rate should have but little influence upon the quantity 
of blood ejected at each systole. From our experiments on the influence of pulse- 
rate on the outflow from the Dog’s heart (see Section IV.), even when a pressure 
was used that gave at the ordinary temperature at which the blood was kept the 
maximum outflow, or very nearly the maximum outflow at each beat, it was found 
that slowing the pulse-rate increases very considerably the outflow at each beat. 
It is true that this may have been owing to the fact that the method used for slowing 
the pulse-rate, viz., by running cold blood through the heart, may have caused more 
or less change in the elastic properties of the ventricular walls. The whole question 
is one that rests as yet, as far as our experiments are concerned at least, upon 
suppositions that lack experimental confirmation. We hope ultimately, after carrying 
out similar experiments upon other animals, to be in a better condition to speak on 
the subject. 
II. 
Influence of variations of arterial 'pressure upon the ivorlc clone by the heart. 
In the experiments made upon this point the venous pressure was kept constant at 
15 or 20 centims. of defibrinated Calf’s blood (117 to 15’6 millims. of mercury); the 
arterial pressure was varied by simply raising or lowering the end S of the outflow 
tube t, (Plate 7). That variations of arterial pressure have no direct effect on the 
pulse-rate of the isolated Dog’s heart has been clearly proved by Professor Martin’s 
experiments. It would have been preferable, perhaps, to have kept the venous 
U 2 
