700 
THE VETERINARY ART IN INDIA. 
I rut he middle of the eye there is a thin, round, muscular mem- 
brane, called the iris ; and that which appears a black spot in 
the centre of it, and of an oblong shape in the horse, is an aper- 
ture termed the pupil, through which the rays pass. This mem- 
brane is radiated and gives colour to the eye, as brown and blue 
in the human subject, and wall-eye, brown, or cinnamon-colour, 
in the horse, which last is observed to be most free from dis- 
ease. It likewise dilates and contracts according to the propor- 
tion of light the eye is exposed to. Thus, on examining the pupil 
of a horse, the future state of vision may be prognosticated with 
some degree of certainty. On a horse being brought from a dark 
stable and exposed to a considerable glare of light, the pupil will 
contract, if his eye be sound, in order to diminish the number of 
rays which at first stimulate the optic nerve. On the contrary, if 
any of the humours be cloudy, he expands his pupil to receive all 
the rays possible, as the objects pass on to the optic nerve in a 
very confused form, having the same effect as looking through a 
telescope immediately after the glasses have been breathed on. 
The very delicate structure and transparency of these parts 
will in some measure account for the obstinacy which frequently 
attends the cure of diseases; why they are so liable to a return 
of the complaint ; and why impaired vision must inevitably be the 
consequence of these returns. The circulation of these parts is 
conducted by very small capillary tubes, conveying only the finest 
and most transparent particles of blood. If the circulation of 
these parts is much increased, as in local inflammation, and the 
blood rushes with a great degree of impetus, the consequence 
is a rupture of the capillary tubes, and an admission of red par- 
ticles of blood to membranes and humours w r hich were before 
perfectly transparent ; and on the inflammation subsiding, and 
the parts being in some measure restored to their primitive order, 
the eye will be left in nearly the following state : — the delicate 
mechanism of the capillary vessels strained, ruptured, and de- 
prived of their tone, by which the eye will be very liable to be 
again affected ; and the beautiful transparency of its parts slightly 
obscured, by having circulated grosser fluid than nature designed 
them to do. 
I cannot omit mentioning a muscle of the horse’s eye in this 
place, as it tends to confirm an opinion adopted at the Veterinary 
College against that of farriers, &c. Most cases of inflammation 
of the eye are said by the latter to arise from blows, or some ex- 
ternal violence which the animal has received. I will venture to 
affirm that not one case in twenty arises from that cause; for the 
eye, in its natural position, is in a great measure defended by its 
orbit ; but on any violence being threatened the animal, or any 
