146 
MESSRS. W. H. HOWELL AND F. DONALDSON 
a longer time to traverse, as for instance, those in which the portal system is included, 
some a shorter time. 
If we take the ratio of the weight of blood pumped out at each systole to the body 
weight as given by Yolkmann, and with which that of Vierordt is almost identical, 
viz., ’0025, the time necessary for a complete circulation in the hypothetical case 
above would be about 15 seconds. 
The time obtained by such a calculation represents in reality the average time for 
all the numerous possible paths. Of the various paths open for the blood to take 
after leaving the heart, those in the course of which only two capillary regions are 
interposed will practically take about the same time to traverse, the velocity in 
the arteries and veins being such that mere distance from the heart will add but 
little to the time required. For that large quantity of blood which, sent out from the 
left ventricle, returns to it again only after having passed through three capillary 
regions, the time required for circulation will naturally be greatly increased. Hence 
the average time for all the different paths should be somewhat greater than the 
time found necessary by Vierordt for the jugular-femoral path, as is the case with the 
time obtained by our calculation ; certainly not less, as would follow if Volkmann’s 
ratio were correct. 
Another consideration which influences us in supposing that the maximum outflow 
at each systole from the isolated heart is about the normal outflow during life, is 
based on tire pressure in the left auricle. 
As far as we know, no one has ever determined the pressure in the left auricle 
during life without opening the thorax, but it is fair to suppose that it is as great 
as that in the right auricle. The maximum pressure in the right auricle of the 
Dog, according to an experiment of Goltz and Gaule (5), is about 19'6 millims. of 
mercury. We determined in one of our isolated hearts the pressure in the left auricle 
(in a way described in Section III.) for each different venous pressure used on 
the right side. According to this experiment the mean pressure in the left auricle 
when the feeding-flask stood at a height of 60 centims. above the right auricle, was 
only 16 millims. of mercury, the maximum pressure 20 millims., and consequently 
no greater than that which it is probable exists during life. Our maximum out¬ 
flow was obtained in all cases either at or below a venous pressure on the right 
side of 60 centims. 
The mean ratio of the weight of blood thrown out at each systole to the body 
weight, obtained by Yolkmann for the Dog, is - 0027, or about twice the ratio 
obtained from our experiments. That there could have been an error of such 
magnitude in the method employed by us does not seem at all possible, and when 
we consider, on the one hand, the very uncertain data upon which Volkmann’s 
results are based and the complexity of the disturbing conditions, and, on the other 
hand, the comparative simplicity and directness of the method we have used, its 
freedom from sources of error, and the agreement of different experiments, we are 
