In wounds of the eye there is occa sionally an extension of the inflammation to the opposite eye, and this is commonly spoken of as by sympathy. Inflammation, especially in the severe forms which sometimes occur, can scarcely owe its origin to nervous influences alone, and this conclusion is confirmed by the fact that the inflammation may progress after the eye primarily affected has been removed. Mackenzie first suggested that the inflammation travelled up the optic nerve to the chiasma and down the other nerve to the opposite eyeball. This view has been recently amplified, and it has been asserted that microbes propagate up the sheath of one optic nerve and down that of the other so as to produce the inflammation. This would explain how the affection of the second eye always occurs considerably after that of the first, and how removal of that primarily affected does not always stop the disease. One of the principal difficulties in the way of accepting it is that the inflammation does not begin in the optic nerve and retina but in the ciliary body and iris. The explanation seems, however, generally accepted for cases of severe inflammation, but slighter inflammations and functional irritations of the eye may be produced reflexly.

The inflammation begins in the iris and ciliary body, and has generally the characters of an iritis and cyclitis. Predisposition or susceptibility seems to have considerable influence in determining the occurrence of sympathetic inflammation.