DISEASES OF THE OX AND SHEEP. 613 



Now in gutta serena, an aflfection which is also known as 

 amaurosis, and in popular phraseology as glass-eye, there is a loss 

 of nerve power, the retina not being capable of receiving, and 

 the optic nerve not able to transmit, the impression of the image 

 of an object to the brain. Nevertheless, the eye looks as clear 

 ■and bright as in health. The malady consists in a loss of power 

 on the part of the retina and the optic nerve ; but the cause of 

 the impairment of nerve-power is not well known. 



A human being afflicted with this disorder is conscious of an 

 increasing diminution of his power of vision, and an experienced 

 and skilful oculist may be able to discover even the early 

 changes of the retina which correspond with the beginning of 

 the complaint. Animals also may, by the abnormal characters 

 of their movements, show that they are losing their eyesight. 

 For instance, in the case of a horse, shying, although in 

 many instances it may merely indicate alarm, may be a sign 

 of some defect of vision, and possibly in some cases at least of 

 this particular disorder which we are considering. Again, in a 

 very few instances, if a horse or other animal makes suddenly a 

 movement as if startled, or markedly points its ears and moves 

 its head towards a person approaching or an advancing object, 

 the suspicion that something is wrong with the eyesight may be 

 entertained. 



A horse suffering from Gutta Serena will appear more than 

 usually shy when being handled about the head. If brought to 

 the light, he turns his head towards it; he also lifts his feet 

 higher than is usual, and will run up against a wall if directed 

 to it. The pupil is much dilated, round, and motionless, 

 and the eyes are widely open, glassy, and staring. Even when 

 the full glare of the sun, or a very strong artificial light, 

 falls upon the eye, the pupil does not contract as in the case of 

 a healthy horse, but remains oval (with long axis of the oval 

 the transverse) and large. 



By the aid of the ophthalmoscope, an experienced observer may 

 be able to see the optic disc, and to note any changes which may 

 have taken place in its appearance, more particularly in regard 

 to colour, and to the size of the vessels which branch on its 

 surface. If the eye of a horse is healthy, the disc when thus 

 seen appears to be light orange in colour, and the blood-vessels 

 are seen most distinctly on the margin of the disc. Gutta 



