OF FARRIERY. 



87 



line lens, and their formations appear to be 

 that the circumference of the coat ending 

 here, to embrace the lens ; it, by which 

 means is thrown into folds, in order to fit ; 

 something similar to the gathering of a shirt, 

 at the wristband. 



The vitreous humour is of a peculiar con- 

 struction ; though it appears to be a kind of 

 jf.lly, it is not; but nearly of the same fluidity 

 is the aqueous humour. This appearance 

 arises from its being contained in cells, and 

 not in a single capsular bag. This is proved by 

 breaking the cells, the fluid then drops freely. 

 It is also admirably formed, for being in 

 contact with the expansion of the optic 

 nerve, as it cannot alter its position, or be in- 

 jured by pressure. 



VISION. 



The phenomenon of vision is at once curious 

 and grand. In the first place, all objects to 

 be seen require a sufficient quantity of light 

 to render the nerve sensible ; though different 

 animals require different degrees, man of all 

 .■tnimals requiring most, plainly demonstrated 

 from the construction of the eye, it having a 

 small transparent cornea, and a black pig- 

 ment ; thus proving we were intended to sleep 

 much, and being gifted with brain and reason, 

 we have no occasion to prowl about at night ; 

 for, in comparison with other animals, many 

 of our senses are imperfect, such as hearing, 

 seeing, and smelling; and so are our arms for 

 flying ; but we are as perfect as nature in- 

 tended ; that is, we do not require further pro- 

 tection. The vision to be perfect, must be 

 painted on the retina ; and here is a curious 

 fact, that though we have two eyes, we see only 

 one object : yet there is an object painted on 

 each retina, but only one on the setisorium : 



but having only one sensorium, so that as long 

 as the object is the same, there is only one im- 

 pression formed ; but immediately objects 

 change, there are different impressions formed. 

 All objects on the retina are painted upside 

 down, so that it is evident the rays of light 

 cross each other ; for they meet in a point near 

 the lens, and proceed through the vitreous hu- 

 mour nearly in the same right lines. This is 

 proved by taking off the sclerotic coat, then 

 placing a sheet of paper behind, with a candle 

 before, the image becomes perceptible upon 

 the paper. I have every reason to believe 

 that objects are represented on the sensorium 

 as they really are ; and this appears no more 

 difllcult, than when theie is an object upon 

 each retina, there should be but one upon the 

 brain : but to speak more correctly, I think 

 the impression upon the sensorium, is no 

 more than the knowledge that the objects 

 are there ; not really that there is an 

 impression made there similar to that on the 

 retina. 



Having considered the structure and general 

 laws of the eye, I shall proceed to explain the 

 alterations to which the eye is liable ; a 

 knowledge of the parts was first necessary to 

 be enabled to discover how alteration is pro- 

 duced. The eye of man is liable to many 

 diseases, the Horse but few ; but before we 

 enter on the diseases of the eye, I will make a 

 few observations on the 



SOUND EYE. 



As a blind Horse is well known, it is highly 

 essential to be thoroughly familiar with the 

 appearance of a sound eye ; for it is only 

 gained from practical experience. There is a 

 peculiar kind of eye which dealers call a sour 

 eye ; this kind of eye the dealers know very 



