SECTION II.

INFLUENZA EPIDEMICS SINCE 1893 47

Occurrence since 1893 47

Period from 1893–1918 47

Increase in 1900–1901 49

Period from 1901–1915 51

Influenza in 1915–1916 55

Influenza between 1916 and 1918 58

The pandemic of 1918 59

Date of first increased prevalence in various localities 65

Influenza in China 80

Autumn spread in the United States 81

Recrudescences 87

Recurrences in the winter of 1919–1920 89

The winter of 1920 90

Incubation period 95

Predisposing causes 96

Periodicity 97

Virulence enhancement 108

Meteorologic conditions 113

Secondary invaders 114

Origin of the 1918 pandemic 116