ON THE HEART OF THE DOG. 
141 
the aorta will be balanced by a proportional under-valuation of the velocity in it, 
and inversely. While this may be true of the aorta as compared with the carotid 
alone, it will hardly hold with regard to the intervening vessels, the second branch 
of the third vascular section for instance, any mistake in the diameter of which 
will introduce an error into the calculation. Vierordt’s method (2) is based, like that 
of Volkmann, upon the proposition that the mean velocity in the arterial system 
is inversely as its sectional area. He determined the mean velocity in the carotid 
by means of his hsemotachometer, obtaining results for the Dog which agree very 
closely with those obtained by Volkmann. Knowing the velocity in the carotid, 
and accepting the measurements given by Krause for Man of the diameter of the 
carotid, the sub-clavian, the innominate, and the aorta beyond the point at which the 
innominate is given off, he deduced the quantity of blood flowing through the 
sectional area of each of these arterial trunks in a second. The quantity of blood 
flowing per second through the sectional area of the ascending limb of the aortic arch 
was taken as equal to the sum of these quantities plus 4 cub. centims. allowed for the 
coronaries. Knowing the number of systoles occurring in a second, the quantity 
thrown out at each systole is easily obtained. Vierordt does not accept the 
supposition of Volkmann that the velocity in each branch of any one vascular 
section is the same, but thinks it safer to assume that the mean velocity in the 
aorta beyond the giving off of the innominate is one-fourth greater than that in the 
innominate. For the ratio of the weight of blood thrown out from the left ventricle 
at each systole to the body weight, he gets a fraction almost identical with that of 
Volkmann : about iwoth. 
Fick, in consequence of the unreliable data upon which the results obtained by 
Volkmann and Vierordt are based, can see in their close agreement only accident. 
His own method (3) while possessing the advantage, as far as Man is concerned, of 
being applicable directly to the human subject, rests, however, upon assumptions 
which cannot be freely allowed. The arm in his method was placed in a sort of 
plethysmograph, by means of which changes in volume occurring at each systole were 
registered upon a revolving drum ; from this curve of volume he constructed a curve 
showing the changes in the strength of the stream in the axillary artery as compared 
with the strength of the stream in the axillary vein, which was taken as a constant. 
From a comparison of this curve with the curve of changes of velocity in the carotid 
of the Horse obtained by Chaveau, he endeavoured to give absolute values to the 
ordinates of his curve, and in this way determined the quantity of blood flowing 
through the sectional area of the axillary artery in a second ; to obtain the quantity 
flowing through the sectional area of the sub-clavian in a second he multiplied by two. 
Then taking the ratio of the strength of stream in the sub-clavian to that in the aorta 
as given by Vierordt, he obtained the quantity of blood flowing through the sectional 
area of the aorta in a second, from which, knowing the pulse-rate, the quantity of 
blood thrown out at each systole was deduced. The mean of his two experiments 
