132 THE SENSORIAL FUNCTION. 



at the sudden blundering of his horse, or injured by one or more stunning falls, 

 has found a very natural although unexpected explanation of it in the blind* 

 ness of one eye, and that perhaps produced through his own fault, by over- 

 riding his willing and excellent servant and causing a determination of blood 

 to the eye, which proved fatal to the delicate texture of the retina. Even for 

 the carriage or the road he is considerably deteriorated, for his field of observation 

 must be materially lessened. 



Let the size of both pupils be carefully noticed before the horse is removed 

 from the stable, and, as he is led to the door, observe whether they both con- 

 tract, and equally so, with the increase of light. If the horse should be first 

 seen in the open air, let it be observed whether the pupils are precisely of the 

 same size ; then let the hand be placed over each eye alternately and held 

 there for a little while, and let it be observed whether the pupil dilates with 

 the abstraction of light, and equally in each eye. 



Hanging from the upper edge of the pupil of the horse, are two or three 

 round black substances, as large as millet seeds. When the horse is suddenly 

 brought into an intense light, and the pupil is closed, they present a singular 

 appearance, as they are pressed out from between the edges of the iris. An 

 equal number, but much smaller, are attached to the edge of the lower portion 

 of the iris. Their general use is probably to intercept rays of light which 

 would be troublesome or injurious, and their principal function is accomplished 

 during the act of grazing. They are larger on the upper edge of the iris, and 

 are placed on the outer side of the pupil, evidently to discharge the same func- 

 tion which we have attributed to the eyelashes, viz. to obstruct the light in those 

 directions in which it would come with greatest force, both from above and even 

 from below, while, at the same time, the field of view is perfectly open, so far 

 as it regards the pasture on which the horse is grazing. 



In our cut m gives a duplicature of the iris, or the back surface of it. This 

 is called the uvea, and it is covered with a thick coat of black mucus, to arrest 

 the rays of light, and to prevent them from entering the eye in any other way 

 than through the pupil. The colour of the iris is, in some unknown way, con- 

 nected with this black paint behind. Wall-eyed horses, whose iris is white, 

 have no uvea. 



We now arrive at a body on which all the important uses of the eye mainly 

 depend, the crystalline lens, g, so called from its resemblance to a piece of crys- 

 tal, or transparent glass. It is of a yielding jelly-like consistence, thicker and 

 firmer towards the centre, and convex on each side, but more convex on the 

 inner than the outer side. It is enclosed in a delicate transparent bag or capsule, 

 and is placed between the aqueous and the vitreous humours, and received into 

 a hollow in the vitreous humour, with which it exactly corresponds. It has, 

 from its density and its double convexity, the chief concern in converging the 

 rays of light which pass into the pupil. 



The lens is very apt to be affected from long or violent inflammation of the 

 conjunctiva, and either its capsule becomes cloudy, and imperfectly transmits 

 the light, or the substance of the lens becomes opaque. The examination of 

 the horse, with a view to detect this, must either be in the shade, or at a stable 

 door, where the light shall fall on the animal from above and in front ; and 

 in conducting this examination we would once more caution the intended 

 purchaser against a superfluity of white about his neck. Holding the head of 

 the animal a little up, and the light coming in the direction that has been 

 described, the condition of the lens will at once be evident. The confirmed 

 cataract, or the opaque lens of long standing, will exhibit a pearly appearance, 

 that cannot be mistaken, and will frequently be attended with a change of form 

 —a portion of the lens being forced forwards into the pupil. Although the 



