Interstitial keratitis occurring in a case of Reiter's disease.

interesting and agrees with the general concept developed earlier (Davson and Duke-Elder, 1948) that the barrier separating the blood from the vitreous body is more selective than that separating it from the aqueous humour. The fact that urea, on the other hand, penetrates so readily into the vitreous is interesting: it may be suggested (at this stage purely as a conjecture) that it may, like the sugars, enter by way of the retinal and uveal capillaries, while the other substances may be restricted to the latter.