The neurologist, whose interests are concentrated on diseases of the central nervous system, is likely to overlook the influence of a primary source of trouble elsewhere in the body. When this primary source remains latent, so far as signs of its presence are concerned, the possibilities of error are even greater. Primary carcinoma of the lung is not a common disease and therefore not often thought of, especially in connection with its distant influence on the nervous system. Ewing1 estimated that about 1 per cent of all carcinomas were of this region, and in necropsy examination of 16,578 cases of carcinoma from various sources, 168 cases of carcinoma of the lung were recorded.2 Barron3 recently gave a much higher figure, 9 per cent, and both from his own experience and from a study of the statistics of the last forty years he inferred that the disease was