90 THE SENSORIAL FUNCTIO?.. 



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 blindness of one 

 eye, and that perhaps produced tlirough his own fault, by over-riding his willing and 

 excellent servant, and causing a detennination of blood to the eye, which proved fatal 

 to the delicate texture of the retina. Even for the carriage or the road he is considera- 

 bly deteriorated, for his lield 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 contract, 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 liitle 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 function 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 per- 

 fectly open, so far as it regards the pasture on which the horse is grazing. 



In our cut, w 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, connected 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 cryslalli)ie lens, g, so called from its resemblance to a piece of crystal, or trans- 

 parent 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 oi capsule, and is placed between the aqueous 

 and the vitreous humours, and received into a hollow in the vitreous humour, with 

 which it exactly coiresponds. 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 con- 

 junctiva, and either its capsule becomes cloudy, and imperfectly transmits t!ie ligiit, 

 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 l)een described, the condition of the lens will at once be evident. 

 The confirmed calaract, or the opaque lens of long standing, will exhibit a pearli/ 

 appearance, that cannot be mistaken, and will frequently hv atteiuled with a change 

 of form — a portion of the lens being forced forwards into the i>ii])il. Altliough the 

 disease may not have proceeded so far as this, yet if there is the slightest cloudiness 

 of the lens, either generally, or in the form of a minute spot in the centre, and \\ilh 

 or without lines radiating from that spot, the horse is to be condemned; for, in ninety- 

 nine cases out of a hundred, the disease will proceed, and cataract, or complete opacity 

 of the lens, and absolute blindness, will be tlie result. 



201, says, " The loss of one eye does not enfeeble sight, because ilu; f)'her acquires gremer 

 enero-y, though it luueh contraets ihe field of vision. It is said to render the eoneepiion crrinL', 

 and tiie case of misjudtriueni of distances is the one cotnnioidy broui^ht forward to show this. 

 All I can say on this point is. that the best hunter I ever possessed, a'horse irified with exini- 

 ordinary powers for leapitig, was a one-eyed liorse, and tiiis animal carried me 'hrough ahuuiiiig 

 eeason, without, to my recollection, making one single blunder in leaping." 



