_Healthy carriers and convalescents._—Leichtenstern, who apparently accepted the Pfeiffer bacillus as the cause of influenza, did not believe that the disease could be transmitted by healthy carriers. He based this assumption on the statement, made by Pfeiffer, that the influenza bacillus was only found in acute influenza cases. In the past few years it has been abundantly shown, however, that the influenza bacillus can and does exist on the mucous membranes of healthy individuals. The outbreak in an orphan asylum in New Haven has been previously described. There the probable source of the sharp outbreak of December 27th seemed to be the sister who, on convalescence, resumed her duties in the kitchen. There she inspected and handled the milk served to the children. This suggests the possibility of infection being propagated by convalescents and by food. At present we do not know whether or not a patient remains infectious after the acute symptoms have subsided; we are ignorant as to whether a convalescent patient can transmit the disease; and we are not certain whether the organism found in healthy carriers is virulent or not. The information at hand strongly indicates that apparently healthy individuals may transmit the infection, but the wide distribution of the disease, with multiple possible sources of infection for each individual, and the relative insusceptibility of experimentally exposed individuals has made it impossible so far to answer these questions satisfactorily. GENERAL MANNER OF SPREAD IN INDIVIDUAL LOCALITIES. Having discussed the mode of propagation of influenza among individuals we will follow the disease as it attacks one person after another in a community and study the epidemiologic picture, drawn no longer with the individual as a unit, but with the community as the unit. We must here distinguish between a primary epidemic, the first wave of a progressing pandemic, and the secondary type in which may be grouped those large or small recurrences which light up for a period of one to three or more years after the primary wave. _Primary type of epidemic._—One of the first important statistical studies on this subject was that of P. Friedrich who charted the influenza morbidity in Munich between the months of December, 1889, and February, 1890. Similar observations have been made by Parsons, Raats, Linroth, and H. Schmid, following the 1889 epidemic.