At present the treatment of conjunctival and corneal lesions is almost entirely symptomatic and empirical and, in many instances, thoroughly illogical. Two years ago one of us (G. N. H.) called attention to the frequent misuse of the ointment of yellow mercuric oxide (Pagenstecher's ointment)1and stated that much of its reputation for improving all sorts of conjunctival, corneal and tarsal lesions for which it was not originally intended was probably gained in the days when it was prepared by the apothecaries from mercuric chloride and potassium hydroxide. It is highly probable that the washing of the precipitated oxide was often incomplete and that traces of free alkali remained in the amorphous powder after it was dried. Probably with equal frequency there was an excess of mercuric chloride left, and when this went into solution in the tears a decidedly acid reaction resulted. (ThepHof