is to smite him between the fifth and sixth ribs. Now
that is a very good piece of regional anatomy, for that is the place
where the heart strikes in its pulsations, and the use of smiting there
is that you go straight to the heart. Well, all that must have been
known from time immemorial--at least for 4,000 or 5,000 years before the
commencement of our era--because we know that for as great a period as
that the Egyptians, at any rate, whatever may have been the case with
other people, were in the enjoyment of a highly developed civilisation.
But of what knowledge they may have possessed beyond this we know
nothing; and in tracing back the springs of the origin of everything
that we call "modern science" (which is not merely knowing, but knowing
systematically, and with the intention and endeavour to find out
the causal connection of things)--I say that when we trace back the
different lines of all the modern sciences we come at length to one
epoch and to one country--the epoch being about the fourth and fifth
centuries before Christ, and the country being ancient Greece. It is
there that we find the commencement and the root of every branch of
physical science and of scientific method. If we go back to that time
we have in the works attributed to Aristotle, who flourished between 300
and 400 years before Christ, a sort of encyclopaedia of the scientific
knowledge of that day--and a very marvellous collection of, in many
respects, accurate and precise knowledge it is. But, so far as regards
this particular topic, Aristotle, it must be confessed, has not got very
far beyond common knowledge. He knows a little about the structure of
the heart. I do not think that his knowledge is so inaccurate as many
people fancy, but it does not amount to much. A very few years after his
time, however, there was a Greek philosopher, Erasistratus, who lived
about three hundred years before Christ, and who must have pursued
anatomy with much care, for he made the important discovery that there
are membranous flaps, which are now called "valves," at the origins
of the great vessels; and that there are certain other valves in the
interior of the heart itself.

(FIGURE 1.--The apparatus of the circulation, as at present known. The
capillary vessels, which connect the arteries and veins, are omitted, on
account of their small size. The shading of the "venous system" is given
to all the vessels which contain venous blood; that of the "arterial