Encephalitis lethargica is a disease which has received a great deal of attention during the last few years. The term was first applied by von Economo[208] to a series of cases observed by him in Vienna in 1917, although, as he has pointed out, similar epidemics occurred as early as in 1712. This condition is characterized particularly by lethargy, facial and oculomotor paralyses and a rise of temperature. Cases were reported from England and France by various observers in 1918 and by Pothier, Neal and others in this country in 1919. It has been suggested frequently that the disease is in some way associated with influenza. The pathological findings have also been confused with the African sleeping sickness due to trypanosomes. After such prodromal symptoms as headache, malaise and drowsiness with muscular weakness for a few days, a lethargic or stuporous state usually develops, interrupted occasionally by delirious attacks. Ptosis has been reported, sometimes with immobility of the pupils. Paralyses of the facial and eye muscles are very common. Buzzard and Greenfield[209] after a review of twenty-two cases suggested the following symptomatological classification:—1. Cases characterized by hemiplegia, hemianesthesia, hemianopsia, etc.; 2. Cases characterized by symptoms resembling those of paralysis agitans:—the basal ganglia group; and 3. Cases characterized by a disturbance of the cranial nerve functions. In a publication issued recently by the United States Public Health Service the various types of the disease were summarized as follows:—1. A clinical affection of the third pair of nerves; 2. Affections of the brain stem and bulb; 3. Affections of the long tracts; 4. The ataxic type; 5. Affections of the cerebral cortex; 6. Cases with evidence of spinal cord involvement; and 7. The polyneuritic type with involvement of the peripheral nerves. The Massachusetts Department of Public Health has recently recommended the use of the MacNulty classification, which is quite similar in some respects:— 1. Symptoms of a general nature referable to the central nervous system with no localizing signs. 2. General symptoms with third nerve paralysis. 3. General symptoms with localizing signs of facial paralysis. 4. General symptoms with localizing signs extending down to the cord. 5. General symptoms with polyneuritic involvements. 6. Mild and abortive cases. Autopsies have shown meningeal and cortical congestion, degeneration of the nerve cells, and thickening of the vessels with endothelial proliferation of the glia. Venous thrombosis and multiple hemorrhages also occur. In a study of the cerebrospinal fluid Boveri[210] found the pressure slightly greater in many cases with an increase in the albumen and globulin content and a mild lymphocytosis in occasional cases. The findings are not characteristic or of great diagnostic value. Efforts to isolate the organism responsible for this disease have so far been unsuccessful.