SPECIFIC OR PERIODICAL OPHTHALMIA. 501 



perfectly transparent, yet there will commonly remain some 

 cloudy lines around its circumference. This latter appear- 

 ance should always be particularly attended to, for this is 

 the very last part the opacity quits ; and, w-e believe, this 

 hardly ever wholly leaves the edges of an eye once affected. 

 The eye or eyes, however, thus far recovered, seldom re- 

 main very long sound ; but often are again subject to the 

 diseased action, and the complaint recurs with all its pristine 

 violence. As these attacks are repeated, they leave the eye 

 less and less transparent. The remaining opacity forms a 

 nucleus for future and rapid accretion : sometimes, however, 

 it will remain stationary for a long time, and now and then 

 it never enlarges. But, usually, repeated inflammatory at- 

 tacks succeed each other ; and the whole crystalline lens at 

 last becomes opaque, when the disease takes the name of 

 cataract, in which almost all these inflammations terminate. 

 It is remarkable, likewise, when the process of forming cata- 

 ract has become fixed and regular within the crystalline lens, 

 active inflammation usually leaves the eye, and seldom again 

 returns. Occasionally it terminates more destructively ; the 

 crystalline lens may be pushed from its capsule against the 

 membrane of the aqueous humour ; sometimes the pupil is 

 torn, and the iris hangs ragged, or adheres to neighbouring 

 structures; and more rarely the eye is thoroughly disorganized. 

 Causes. — It has been conjectured, that the remote cause 

 of this disease arises from the plethora which takes place in 

 horses at the adult period ; that is, when they have just 

 attained their growth, at which time it is observed they 

 are more frequently attacked by it ; for until this age the 

 blood has not only to nourish the body, but to increase 

 it also by the addition of parts ; but after maturity, having 

 only to support the organs it has already formed, there 

 must be a superabundant quantity thrown on the system : at 

 this period, therefore, the vascular action is strong, and 

 much subject to distention. This theory, however inge- 

 nious, is by no means sufficient to account for the consti- 

 tutional predisposition so evident to this disease ; it is by 

 no means confined to the adult period ; it has been wit- 

 nessed in colts far from the adult state ; and even barring 

 this objection to its corr-ectness, it yet remains to be ac- 

 counted for, why the eye should be, of all the organs, the 



