eats into bloud easie to
be known, if we consider, that it is distill'd by passing and repassing
the heart, perhaps more then one or two hundred times a day? And what
need we ought else to explain the nutrition and the production of divers
humours which are in the body, but to say, that the force wherewith the
bloud in rarifying it self, passeth from the heart towards the
extremities or the arteries, causeth some of its parts to stay amongst
those of the members where they are, and there take the place of some
others, which they drive from thence? And that according to the
situation, or the figure, or the smalnesse of the pores which they
meet, some arrive sooner in one place then others. In the same manner
as we may have seen in severall sieves, which being diversly pierc'd,
serve to sever divers grains one from the other. And briefly, that which
is most remarkable herein, is the generation of the animal spirits,
which are as a most subtil wind, or rather, as a most pure and lively
flame, which continually rising in great abundance from the heart to the
brain, dischargeth it self thence by the nerves into the muscles, and
gives motion to all the members; without imagining any other reason
which might cause these parts of the bloud, which being most mov'd, and
the most penetrating, are the most fit to form these spirits, tend
rather towards the brain, then to any other part. Save onely that the
arteries which carry them thither, are those which come from the heart
in the most direct line of all: And that according to the rules of the
Mechanicks, which are the same with those of Nature, when divers things
together strive to move one way, where there is not room enough for all;
so those parts of bloud which issue from the left concavity of the heart
tend towards the brain, the weaker and less agitated are expell'd by the
stronger, who by that means arrive there alone.

I had particularly enough expounded all these things in a Treatise which
I formerly had design'd to publish: In pursuit whereof, I had therein
shewed what ought to be the fabrick of the nerves and muscles of an
humane body, to cause those animall spirits which were in them, to have
the power to move those members. As we see that heads a while after they
are cut off, yet move of themselves, and bite the ground, although they
are not then animated. What changes ought to be made in the brain to
cause waking, sleeping, and dreaming: how light, sounds, smels, tas