The epidemic disease known as influenza is believed to be due to an
undetermined organism which causes an infection that lowers the
resistance of the body as a whole, and of the respiratory organs in
particular. This allows the invasion of other pathogenic
micro-organisms. The most important complicating infections are due to
the influenza bacilli, different strains of pneumococci and different
varieties of streptococci. Some careful observers regard certain of
these organisms as the primary cause.
In each case, one or several of these micro-organisms may be present. In
different portions of the country the dominating variety of organism has
been found to differ.