2. Indefinite knowledge and conflicting evidence regarding site and manner of origin.
3. Apparent transmission chiefly or entirely through human intercourse.
4. Rapid spread over all countries, the rapidity roughly paralleling the speed of human travel.
5. Rapid evolution of the disease in the communities where outbreaks occur, with nearly equally rapid subsidence after several weeks’ duration.
6. Apparent lack of dependance on differences of wind or weather, seasons or climate.
7. Generally low mortality in contrast to enormous morbidity. Variation in the incidence of disastrous secondary infections.
8. Tendency to successive recurrences at short intervals.
SECTION II.
Influenza Epidemics Since 1893.
In this section of our report we will describe with as great accuracy as our sources of information will permit, and in as great detail as space will allow the events which have led up to the epidemics of 1918–20 and the various phases of the epidemics themselves. Points of similarity with previous epidemics will be made obvious; the differences, when of significance, will be described and studied in detail.