In the winter of 1918-1919 a disease of the central nervous system appeared suddenly in various parts of the United States. This disease seems never to have been recognized previously in this country. What is generally believed to be the same condition, however, occurred in Vienna in the winter of 1916 (Economo 1917); in France in April, 1917 (Cruchet, Moutier and Calmette 1917), and in England (Harris 1920; A. J. Hall 1918) and Germany (Moewes 1920) in the spring of 1918. While the clinical symptoms are varied and a number of different types of the disease have been distinguished by some observers (MacNalty 1918), the pathologic lesions present a close agreement in cases studied in Austria, France, England and the United States, and are sufficient in the opinion of most writers to establish lethargic or epidemic encephalitis as a distinct disease (Flexner 1920; Stern 1923). Flexner (1924), indeed, regards the current pandemic of epidemic encephalitis as the first appearance of