ll cases quite clear and definite.
The tela aranea is said to take its origin from the retina, the retina
from the optic nerve, and the latter from the rethi (rete, network)
involving the substance of the brain. The cornea arises from the
sclerotic tunic, the uvea and secundina take their origin from the
pia mater, and the conjunctiva from a thin pellicle or membrane which
covers the exterior of the cranium and is nourished by a transudation
of the blood through the coronal suture. This pellicle is also said
to have a connection with the heart, which arrangement furnishes a
decidedly curious explanation of the mechanism of sympathetic and
maudlin lachrymation. For, as Gilbert tells us, when the heart is
compressed this pellicle is also compressed, and if any moisture is
found beneath the pellicle it is expressed into the substance of the
lachrymal gland by the constriction of the heart, and men in sorrow
therefore shed tears. And again, if the heart is much dilated or
elevated (by joy), this pellicle is also dilated or elevated, and
if any moisture is found beneath it, it is expressed in the form of
tears. Accordingly, men who are too joyful shed tears. Still further,
drunken men, who are notoriously "moist," and have a superfluity of
fluid between the pellicle and the skin of the cranium, are prone to
weeping on slight provocation, and their tears are nothing more than
an expression of this moisture, which makes its exit, not through the
substance of the eye, but through the "lachrymal angle." Q.E.D.

This odd demonstration is followed by a succession of optical
questions, which are discussed and answered in true scholastic style,
with no little acuteness of observation. Thus: "_Utrum visus fiat
intus suscipiendo?_" Is vision accomplished by something received into
the eye? "_Utrum color fit de nocte?_" Does color exist at night? To
the latter question Gilbert replies that in the darkness color exists
in posse, but not in esse. Again: "Why do some animals see at night,
some in the day only and some only in the twilight?" This phenomenon
he ascribes to "the clearness and subtilty of the visual spirits, or
to the strength, weakness, grossness or turbidity of the organs of
vision." Some animals, he says, have (visual) spirits, subtle and
clear as fire, and these animals see perfectly at night because the
visual spirits (_spiritus visibilis_) are sufficient to illuminate the
external air. "Why do objects in water seem near