with in tumours of every part of the cerebral hemispheres, of the pons Varolii, the crura cerebri, the cerebellum. I am not aware that neuritis has been found in tumours limited to the medulla below the pons. It is common in tumours of all parts of the hemispheres. Dr. Clifford Allbutt thinks that tumours of the anterior lobes are more uniformly attended with neuritis than those of other parts, but I have seen a large growth in the anterior hemisphere with normal discs throughout.
Nor does the nature of the tumour apparently influence the development of neuritis. It occurs with every variety— glioma, sarcoma, tubercle, syphiloma. The most frequent forms of tumour are those which are met with most frequently in association with optic neuritis; and they are also those in which neuritis is most frequently absent—syphilomata, tubercles, and gliomata.
The size of the tumour also seems to have little influence in producing neuritis. I have twice seen syphilomata the size of half an egg without optic neuritis. One of the largest intra-cranial tumours I have met with was a sarcomatous growth, the size of the closed fist, growing from the dura mater, and compressing, not invading, the brain over the posterior portion of the parietal lobe, a tumour which must have increased the intra-cranial pressure as much as it is ever increased directly by a growth, and in this case the discs, repeatedly examined from soon after the onset of the symptoms until death, about six months later, were perfectly normal. On the other hand, Benedikt has recorded a case of well-marked neuritis with much swelling and hæmorrhages, due to a tubercle of the pons Varolii no larger than a cherry. There were no signs of meningitis.
The chief facts at present known regarding the mechanism by which optic neuritis is produced have been already discussed (p. 63). Some points having special reference to tumour may be again adverted to. It is clear from the facts stated above, and a long list of similar cases might be given, that encephalic tumours do not cause neuritis by the direct effect of their mass on the intra-cranial pressure. Perhaps no form of cerebral tumour is attended with optic neuritis in a
