“Provisionally, however, we will hold until the proof has been obtained by bacteriological methods that influenza nostras and influenza pandemica are two entirely different diseases, just as are cholera nostras and asiatica. Accordingly, we will divide the diseases designated as influenza in the following way:

“1. Influenza vera, caused by the Pfeiffer bacillus.

“2. The endemic-epidemic influenza vera which arises from the germ remaining after the spread of the influenza pandemic and which is caused by the same germ, the bacillus of Pfeiffer. The duration of this endemic state of influenza vera may last years in single localities.

“3. The endemic influenza nostras, or pseudo-influenza or catarrhal fever, commonly called grip, a disease sui generis. The germs causing this disease are at present as little known as are those of cholera nostras.”

Parkes, in 1876, recognized these possibilities: “The exact spot has not been made out. Two opinions prevail. First, one focus; second, many foci. Each nation, in turn, attributes the disease to its neighbor and from the names so given one can follow the direction of the epidemic.” Noah Webster believed that in 1698, 1757, 1761 and 1781 it originated first in America. Hirsch believed that some of the epidemics had probably originated in North America.

We find then that after the pandemic of the last century the same epidemiologic questions had arisen that have come into such prominence during the present period. As a rule those who have quoted the epidemiologists of 1890 to 1900 have mentioned the first hypothesis and have failed to allude to the fact that the other two were considered. So we see that the subject was by no means settled even at that time, and that if we should discover that the 1918 pandemic cannot be traced to a single endemic focus our results will not be absolutely contradictory to those of the last century.

Returning to a consideration of the period 1916–1918, we observe from reference to Frost’s diagram that in the spring of 1918 there was a sharp and general rise in mortality from influenza and pneumonia. Frost reports that in the larger cities on the Atlantic seaboard this increase occurred generally during January, February and March, when pneumonia mortality normally reaches its maximum. The increase was not so evident in all these cities as it was in New York City. In the rest of the country, especially in the Central and Western States, the increase occurred in April, a month during which pneumonia mortality is generally on the decline, and was sufficient to constitute an unmistakable departure from the normal. The increased mortality rate extended quite generally into May and in some areas still longer. This is the first increase after 1916 that is pictured in the mortality statistics for the country at large.

There are some who believe that they saw influenza in mild form in the United States army in the year 1917. V. C. Vaughan has investigated this possibility and from a study of the sick and wounded charts decided that there was no relation between influenza and the pneumonia which was prevalent in 1917, and which usually was secondary to measles, being caused by the streptococcus in the majority of localities. The lack of association between influenza and pneumonia in 1917 and the direct association in 1918 is well brought out by a comparison of the figures in the two following charts, prepared by V. C. Vaughan:

Pneumonia as a Sequel to Respiratory Diseases.
(All troops in United States in 1917.)
Primary diseases. No. of cases. No. of cases followed by pneumonia. Per cent. of cases followed by pneumonia.
Measles 47,573 2,075 4.37
Scarlet Fever 1,966 54 2.75
German Measles 8,982 39 0.43
Bronchitis 41,233 20 0.049
Influenza 32,248 19 0.059
Meningitis 1,027 13 1.27
Tonsillitis 43,021 7 0.016
Pulmonary tuberculosis 6,799 6 0.088
Laryngitis 4,633 2 0.043
Diphtheria 1,163 1 0.086
Mumps 21,725 0 0.000
Pharyngitis 8,096 0 0.000
Influenza and Pneumonia in Last Four Months of 1918.
Number of cases of influenza 338,343
Number of cases of influenza followed by pneumonia 50,700
Number of deaths from influenza-pneumonia 17,700