the left cavity of the heart, and a tube through which it passes from the
arterial vein into the grand artery without passing through the lung. In
the next place, how could digestion be carried on in the stomach unless
the heart communicated heat to it through the arteries, and along with
this certain of the more fluid parts of the blood, which assist in the
dissolution of the food that has been taken in? Is not also the operation
which converts the juice of food into blood easily comprehended, when it
is considered that it is distilled by passing and repassing through the
heart perhaps more than one or two hundred times in a day? And what more
need be adduced to explain nutrition, and the production of the different
humors of the body, beyond saying, that the force with which the blood, in
being rarefied, passes from the heart towards the extremities of the
arteries, causes certain of its parts to remain in the members at which
they arrive, and there occupy the place of some others expelled by them;
and that according to the situation, shape, or smallness of the pores with
which they meet, some rather than others flow into certain parts, in the
same way that some sieves are observed to act, which, by being variously
perforated, serve to separate different species of grain? And, in the last
place, what above all is here worthy of observation, is the generation of
the animal spirits, which are like a very subtle wind, or rather a very
pure and vivid flame which, continually ascending in great abundance from
the heart to the brain, thence penetrates through the nerves into the
muscles, and gives motion to all the members; so that to account for other
parts of the blood which, as most agitated and penetrating, are the
fittest to compose these spirits, proceeding towards the brain, it is not
necessary to suppose any other cause, than simply, that the arteries which
carry them thither proceed from the heart in the most direct lines, and
that, according to the rules of mechanics which are the same with those of
nature, when many objects tend at once to the same point where there is
not sufficient room for all (as is the case with the parts of the blood