When I was requested by your secretary to read a paper before this Section it occurred to me that it might be a fitting opportunity to familiarize neurologists with the classification of diseases of the optic nerve as used by ophthalmologists, and to attempt to elucidate, in a measure, the significance of changes in these structures in connection with diseases of the central nervous system. It may seem, perhaps, that such an exposition is unnecessary, in view of all that has been said and

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... n on ophthalmic neurology, but experience has taught that even in this well-traveled path there is still a lack of perfect understanding between ophthalmologists and neurologists. This has arisen in a large part, perhaps, by reason of the uncertainty which exists at times in the mind of the ophthalmologist when he is requested by the neurologist to render a report on any given case. He is aware that something definite is demanded of him and that his testimony is often awaited as corroborative evidence in the diagnosis of some obscure lesion, and yet it frequently happens that he does not feel able to pronounce with certainty that a nerve is actually inflamed or to discriminate between a primary or a consecutive atrophy. Indeed, a direct answer to these questions is often impossible. Even the physiologic variations in the appearance of the nerve are very great, and many times an inflammation or an atrophy may be simulated by what is in reality only a likeness to these conditions. When dealing with such uncertainties, therefore, the ophthalmologist often feels unable to do more than describe to the neurologist what he sees and. without attempting any positive 'diagnosis of the conditions with which he is confronted, permits the neurologist to draw his own deductions from the findings which are reported to him. Then, too, ophthalmologists are not wholly united in their classification of diseases of the optic nerve, and the employment of terminologies, which are often different, render the clear conception of the entire subject of inflammation and atrophy confusing and difficult of comprehension. Koenigshofer, following the fundamental division which is adopted in describing diseases of the spinal cord, has recently proposed a classification according as the inflammation of the nerve presents a focal or more generalized lesion. Thus under the focal or transverse form are included all varieties of inflammation of the nerve, those originating from the sheath and from the interstitial tissue as well, which traverse its entire cross section and spread longitudinally as well as transversely. Under the generalized group, on the other hand, are collected those processes which show themselves from the first as definite defects in the visual field, as, for example, involvement of the papillo-macnlar bundle, with well-defined central scotoma. Lesions in the nerve included in the first group follow infectious processes, those in the second, intoxication and nutritional processes. inflammation according to its site in the axis of the nerve, the term "papillitis" being used to designate all forms of inflammation which affect the head of the nerve and produce visible ophthalmoscopic changes while involvement of the nerve in its deeper portion is described by* the terms "descending" and "retrobulbar" neuritis; as frequently in the early stages of these latter types there is no ophthalmoscopic evidence of the inflammation, its existence must be determined by other means. Although this division of optic neuritis was made by von Graefe, subsequent investigations have shown that there is no pathologic evidence to support such a base of distinction, for both papillitis and descending neuritis continually merge into each other, and even clinically, as Gowers demonstrated many years ago, the aspect of the disc may assume at one time the characteristics of descending neuritis and at another those of papillitis. In true papillitis, however, the swelling of the disc is very great, and while in the early stages the veirs less frequently present dilatations than in neuritis from meningitis, the retinal vessels become later greatly dilated and tortuous, especially the veins. Hemorrhages and extravasations into the retina are not uncommon. In descending neuritis, on the other hand, the swelling of the papilla is never very pronounced and there is a disposition for the inflammation to spread to the adjacent retina. The changes in the disc, too, are often most intense at the periphery, the center being but slightly involved. Hemorrhages and extravasations are not uncommon, and the vessels are. not kinked as they pass over the edges of the nerve, as is so often the case in intense degrees of neuritis. When the swelling of the nerve in papillitis assumes a height of 2 D. or more the arbitrary expression of choked disc is assigned to it, and the term neuroretinitis is given to those cases in which the inflammation of the nerve has extended so as to involve rather a large area of retina. It is unnecessary to dwell here on the significance of the relation which choked disc bears to brain tumors, as that phase of the subject has already been largely discussed elsewhere, nor, indeed, need^f urther reference be made to descending neuritis other than to remark that it is chiefly observed in children, where it is usually caused by acute and chronic meningitis, by tubercle of the brain and by hydrocephalus. Deformities of the skull also, particularly peaked skull, may sometimes give rise to this form of neuritis. Attention must, however, be called to spurious optic neuritis, for, as a consequence of a congenital peculiarity of the optic papilla, healthy nerves at times may exhibit the signs of neuritis. Vision in these cases, however, is normal, and no further change is manifested even after years of observation. Lesser degrees of swelling, though occasioned by hyperemia, are seen in hypermetropic eyes, in commencing toxic retrobulbar neuritis and in various types of chronic insanity. This appearance of the nerve is designated rs simple congestion and is indicative of a stasis in its circulation. From a diagnostic standpoint both spurious optic neuritis and simple congestion are especially significant when the changes are notably greater in one eye than the other. To the two main divisions of inflammation of the optic nerve must he added retrobulbar neuritis, which may be regarded as a mixed condition of interstitial inflammation of the nerve with atrophy. In this variety of neuritis there are at first either no ophthalmoscopic signs or merely those of simple congestion. Later,