52 
pliny's natukal histobt. 
[Book XL 
iiacing, sparkling, sedate, leering, askance, downcast, or lan- 
guishing. Eej^ond a doubt it is in the eyes that the mind has 
its abode : sometimes the look is ardent, sometimes fixed and 
steady, at other times the eyes are humid, and at others, again, 
half closed. From these it is that the tears of pity flow, and 
when we kiss them we seem to be touching the very soul. It 
is the eyes that weep, and from them proceed those streams 
that moisten our cheeks as they trickle down. And what is 
this liquid that is always so ready and in such abundance in 
our moments of grief, and where is it kept in reserve at other 
times ? It is by the aid of the mind that we see, by the aid 
of the mind that we enjoy perception ; while the eyes, like so 
many vessels, as it were, receive its visual faculties and trans- 
mit them. Hence it is that profound thought renders a man 
blind for the time, the powers of sight being withdrawn from 
external objects and thrown inward: so, too^ in epilepsy, the 
mind is covered with darkness, while the eyes, though open, 
are able to see nothing. In addition to this, it is the fact 
that hares, as well as many human beings, can sleep with 
the eyes open, a thing which the Greeks express by the term 
TiopvjSavri^v, JN'ature has composed the eye of numerous mem- 
branes of remarkable thinness, covering them with a thick coat 
to ensure their protection against heat and cold. This coat she 
purifies from time to time by the lachrymal humours, and she 
has made the surface lubricous and slippery, to protect the eye 
against the effects of a sudden shock. 
CHAP. 55. THE ITATUEE OF THE PUPIL EYES WHICH DO KOT 
SHUT. 
In the midst of the cornea of the eye JS'ature has formed a 
window in the pupil, the small dimensions of which do not 
permit the sight to wander at hazard and with uncertainty, 
but direct it as straight as though it were through a tube, 
and at the same time ensure its avoidance of all shocks com- 
municated by foreign bodies. The pupils are surrounded by a 
black circle in some persons, while it is of a yellowish cast with 
others, and azure again with others. By this happy combina- 
tion the light is received by the eye upon the white that lies 
around the pupil, and its reflection being thus tempered, it 
fails to impede or confuse the sight by its harshness. So 
complete a mirror, too, does the eye form, that the pupil, 
