344 RESEARCHES INTO THE CAUSES OF BLINDNESS. 
junctiva becomes more marked. There is usually an adherence 
between the internal surface of the eyelids and the globe of the 
eye, which draws them with it towards the bottom of the orbital 
cavity. 
CHAPTER II. 
Having thus described some of the morbid lesions engendered 
by an affection which, in the generality of cases, produces loss of 
sight in horses, we are naturally led to trace their further history. 
In that part of the country where most of our observations were 
made, blindness did not appear to result from periodical fluxion, 
properly so called, but was generally caused by an internal ophthal- 
mia, varying in its progress and in the intensity of the symptoms 
that characterize it.' 
Attack . — It is a fact worthy of remark, that the commencement 
of ophthalmia almost always coincides with the period at which the 
horse is first worked ; nevertheless, we have occasionally observed 
it in colts that have not been broken in. It generally appears be- 
tween the third and fifth years, for many horses of that age are 
blind of one or both eyes ; — from the fifth to the seventh year, 
while the eye is undergoing those modifications which we have 
described in speaking of the morbid lesions. 
All seasons do not appear to me to have an equal influence on 
the development of ophthalmia : it is most frequent in spring and 
autumn ; and rainy, foggy, damp, changeable weather appears to 
produce it much more than fine dry settled weather. Indeed, on a 
change from the former to the latter, we have seen the acute 
symptoms disappear almost instantaneously ; but this disappear- 
ance was merely external, and the disease pursued its fatal course 
in the interior of the organs of vision. 
Its debut is not announced by any alarming symptom : the eyes 
look dull and watery; tears flow from them abundantly, which are 
at first clear, but subsequently become thick and viscous, glueing 
together the eye-lashes, and the hair of the face. In some animals 
thus affected, a slight obscurity of the aqueous humour may 
be perceived, on close examination, in the midst of which float 
white specks. Wherever this is the case the sensibility of the 
eye is increased, the slightest motion at a little distance frightens 
the animal, and he shuns and appears terrified by all strange 
objects. These are generally certain precursors of a more or less 
violent inflammation of the conjunctiva, depending in intensity on 
the duties, constitution, and temperament of the animal, and the 
manner in which he is kept and tended. 
The horse is also exposed to another species of ophthalmia, the 
commencement and the progress of which are different to that we 
