The 1920 epidemic of influenza in that country had almost ceased by the middle of March, while that of lethargic encephalitis had greatly decreased. One hundred and forty-one cases of the latter disease appeared in the canton of Zürich alone. Is epidemic encephalitis a disease sui generis or is it a form of influenza? The consensus of opinion has been that it is a separate disease. There is, however, no way of telling how close is the relationship to the influenza itself. If lethargic encephalitis is a sequel to influenza, is it caused by the same germ? Flexner points out that in 1916, when the first cases of encephalitis appeared or at least were recognized in Austria, the epidemic of influenza had not yet appeared. In England, France and the United States the epidemics of the two diseases were more or less coincidental. He believes that little weight can be given the supposed coincidence of influenza and the “sleeping sickness” of 1712, and that it is highly improbable that the semi-mysterious affection, “nona,” which dates from 1890 was definitely a sequel of influenza. He concludes that the outbreak of encephalitis either antedated the pandemic of influenza of 1918, or that the two diseases more or less overlapped; that is, although probably quite by accident, they prevailed concurrently. He prefers for the time being at least to regard them as independent diseases. Crookshank believes that encephalitis lethargica is a distinct disease, but that it occurs frequently as an antecedent of or coincident with influenza, together with increase in the existence of poliomyelitis and certain other diseases. Nevertheless the association in point of time and place between influenza and lethargic encephalitis cannot be lightly overlooked. As we have seen, Flexner’s criticism that encephalitis antedated the influenza is not valid, because the latter was present in 1916. We must await fuller evidence on this subject. SECTION VII. COMPARISON OF INFLUENZA WITH OTHER EPIDEMIC DISEASES. A certain amount of knowledge concerning the epidemiology of influenza may be gained by a comparison of the epidemic features of that disease with those of other epidemic diseases, particularly measles and the exanthemata, meningitis, the plague, and certain diseases of the lower animals. Influenza is described as a disease with distinctive epidemiologic characteristics, the chief of which are found only in epidemic spreads. Thus one of the fundamental characteristics of these epidemics is supposed to be the primary type of wave, the wave characterized by rapid rise, quasi-symmetrical evolution, and a concentration closely grouped around the maximum. “This is found in no other disease. In no other type of epidemic does the curve rise as rapidly to a peak or fall as swiftly, nor is the epidemic completed in as short a time.”