260 THEORY AND PRACTICE 



smaller than the other, at first from retraction in its socket and 

 later from atrophy. The upper eyelid will have an abrupt bend 

 toward its inner angle from the contraction of the levator muscle. 

 The front of the eye has lost its lustre and the depths are green- 

 ish yellow. The ears are alert to compensate for the waning 

 vision. • 



There is no doubt that some specific germ is responsible for 

 periodic ophthalmia, but it has not been demonstrated. The 

 periodicity of the disease is probably due to the manner of de- 

 velopment of the micro-organism, whatever it is, whose genera- 

 ;tions die out from lack of food in the anterior chamber of the 

 eye and the symptoms subside until the spores develop into viru- 

 lent organisms again. 



Etiology. — The causes may be fundamentally attributed to 

 the soil. Damp clays, marshes and bottoms which have fre- 

 'quently been overflowed are potent causative factors. The damp 

 air and wet climate react upon the animal to produce a lym- 

 phatic constitution with an excess of connective tissue, bones and 

 muscle of coarse, open texture, thick skins and gummy legs with 

 profuse long hair. The rank fodders grown on such soils are 

 other causes. Foods act by leading to constipation and under- 

 mining the constitution of the animal, giving it a predisposition 

 to any infection. The period of denition and training is g. 

 fertile exciting cause. The great majority of victims are from 

 2-6 years old. If a horse escapes the infection until after he 

 is six years old, he will probably never get it. The irritation 

 about the head during the eruption of teeth, the unwonted bridle 

 and collar, the stimulating grain diet and the close air of the 

 stable all combine to arouse the latent tendency of the disease 

 in the eye. No one of these conditions would cause the attack, 

 but all together have great bearing as predisposing factors at 

 least. It has been alleged that the specific factor is a germ 

 which is harbored in the marshy district, but it has never been 

 found. 



Heredity is accepted by horsemen as a most potent factor, — 

 one so strong that intelligent horsemen everywhere refuse to 

 breed from either horse or mare that has once suffered from re- 

 current ophthalmia. The French Government even refuses ser- 



