THE CIRCULATION OF THE BLOOD. 241 
THE WoRK OF THE HEART. 
Since the pressure against which the heart works must, as 
we shall see, vary from moment to moment, and sometimes very 
considerably, the work of the heart must also vary within wide 
limits, even making allowance for large adaptability to the bur- 
den to be lifted; for it will be borne in mind that the degree 
to which the heart empties its chambers is also variable. 
If one knew the quantity of blood ejected by the left ven- 
tricle, and the rate of the beat, the calculation of the work 
done would be an easy matter, since the former multiplied by 
the latter would represent, as in the case of a skeletal muscle, 
the work of the muscles of the left ventricle; from which the 
work of the other chambers might be approximately calculated. 
The work of the auricles must be slight, considering that the 
filling of the ventricles is not dependent solely upon their con- 
traction, that they empty themselves very imperfectly, and 
that the tracing on Marey’s curves (Fig. 210), representing the 
effect of their contraction on the intraventricular pressure is 
but small. Notwithstanding, as they largely determine by 
their contraction and the quantity they throw into the ventri- 
cles how full the latter shall be in a given instance, they really 
have a very large share in determining the total work of the 
ventricles and the whole heart. 
The right ventricle, it is estimated does from one fourth to 
one third the work of the left; not, of course, because it throws 
out less blood, for if this were the case the left side of the heart 
must soon become empty, not to mention other disturbances of 
the vascular equilibrium, but because of the relatively less 
resistance offered by the pulmonary vessels, 
All attempts to estimate exactly the quantity ejected by the 
left ventricle seem to show that this varies very greatly, after 
due allowance is made for the imperfection of the methods and 
the great di&crepancies in the results of different observers, 
Perhaps six ounces, or about 180 grammes, may be taken as an 
average for the left ventricle of man. Assuming that his aortic 
blood-pressure is, say 200 mm. of mercury or 3°21 metres of 
blood, the work of this chamber for each beat would be 180 Xx 
3°21, or 578 gramme-metres. If the heart beats seventy times per 
minute, the work for the day would be 578 X 70 X 60 X 24 = 58,- 
262,400 gramme-metres. Or,upon the same basis, and assuming 
that the blood makes up about the one thirteenth of the weight 
of the individual, in a man of 143 pounds, the whole of the 
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