THE NERVOUS SYSTEM 381 



second or third day has a beneficial effect. In very severe cases the 

 ulceration extends through the external coats ; the humour then 

 escapes, and the eye is lost. 



638. Periodic Ophthalmia (inflammation of the internal 

 structure of the eye) differs very much from simple ophthalmia. 

 Formerly it was supposed to come on with the changes of the moon, 

 and got the name of moon blindness, whilst, on account of its tendency 

 to recur, the term ' periodic ' was used. It is not so prevalent as it 

 used to be, and when it does occur, town horses, as a rule, are the 

 sufferers. Its causes are not well understood, but are generally con- 

 sidered to be of a constitutional character ; sudden changes from 

 heat to cold, bad ventilation, and defective drainage are also blamed. 

 In my opinion, one great cause is through an injury brought about 

 by the horse throwing up its head, in a low-roofed stable, and thus 

 hitting itself behind the ears, or it may arise through the infliction of 

 a brutal blow from a stick in that region. Some think it has a 

 hereditary tendency ; such, however, has not been my experience. 

 Symptoms. — As a rule, the attack is sudden, the horse is very dull, 

 hangs its head, and has one or both eyelids closed ; the upper lid has 

 a flat and wrinkled appearance, owing to the eye being pulled back 

 into its socket. The animal cannot bear the light, and, on examining 

 the eye, it is found to be dim, having lost its lustre, the front chamber 

 appearing of a yellowish amber, sometimes a reddish-brown colour, 

 and the pupil can scarcely be seen. Frequent attacks implicate the 

 crystalline lens, and finally end in cataract. 



639. Treatment. — Put the animal into a roomy, well-ventilated, 

 but darkened loose-box, keep it perfectly quiet, and administer mild 

 doses of laxative medicine, say 2 ounces Epsom salts and J ounce 

 cream of tartar, night and morning, in a mash of bran, or as a 

 draught, until the bowels show relaxation. The eye should be 

 sponged with a weak solution of extract of belladonna two or three 

 times a day. This treatment, in some cases, may be all that is 

 required, but in protracted cases I have found great benefit arise 

 from the application of a blister on the side of the cheek or behind 

 the ears. I have had cases in bulls, especially young ones, where 



