The communicability of influenza has been observed by all, and the ease with which it passes from one individual to another noted. One observation made by us was of considerable interest. In a house where a patient lay sick with a severe attack of influenza for nearly three weeks several members of the household passed the door of the sick room a number of times daily, and yet they did not contract the disease. This is in marked contrast with the immediate contact between the two physicians and the young flying officer, who sat in the same railway carriage compartment for four hours. The same observation was made in the hospital among nurses in direct contact with patients. A large number of these contracted the disease, while those not immediately associated with influenza patients almost invariably escaped. This speaks strongly against the idea that the epidemic was a so-called “plague,” or that it passed without intermediate means through the air and pervaded all places. From information thus far at hand it seems, therefore, that the prodromal stage, or stage of incubation, is one which covers about 48 hours, and that it is usually without symptoms unless it be a peculiar prostration which had been described by some patients. It would also appear from the experiences just narrated that it was necessary to be in rather close contact with a patient, so that there could be an exchange of respired air before infection could take place. _Duration of the Disease_ In all descriptions of the disease the duration is spoken of as “several days, more or less,” “a three-day fever,” or “a seven-day fever.” Because of the careful supervision under which the soldiers were kept while in the barracks an excellent opportunity was afforded to note the duration of uncomplicated cases. The shortest time observed was 1 day, and the longest 10 days. The average duration of temperature among 87 soldiers without inflammation of the lungs or other certain complications was 6⅓ days. Among the civilians the shortest time of pyrexia was a few hours only, while the longest in 73 male patients was 14 days, and in 84 female patients was 16 days. The average length of pyrexia in the males was 4⅝ days, and in the females was 5¼ days. While the very definite clinical description of the former epidemics of a so-called uncomplicated influenza seems to have served satisfactorily to the present time, the laboratory studies and the possibly more thorough clinical observations which have been carried out recently in this epidemic make it necessary to present anew the whole disease picture of influenza, with the hope of suggesting a classification more in accord with our present knowledge of the disease. _Forms and Varieties of Influenza_