In ancient times the thoughtful physicians who sought for the reasons and the nature of universal pestilences attributed to elementary powers, such as atmospheric and telluric conditions, an influence upon the entire population. Influenza especially, with its affection of the masses over large areas, fitted in with these ideas. History shows us the manifold variety and often extravagant nature of these hypotheses. The atmosphere was supposed to become foul, poisoned by the exhalations from the soil, etc. We cannot here enter into details concerning these theories, but the idea which the greatest of German philosophers, I. Kant, held in reference to the "noteworthy and wonderful influenza," of which he was a witness in the pandemic of 1782, is worth recounting. He, with his contemporaries, thought that "harmful insects" which were brought through Russian commerce to Europe gave rise to the disease, a conception which the "Medical Council" in Vienna at that time accepted. The authors who severely criticize these ideas should remember that the upholders of this view were decidedly nearer the truth than those who laid the blame of the pestilence on terrestrial magnetism, earthquakes, meteors, and volcanic eruptions, phlogistic air, electric fluctuations, and similar causes. Yet together with these speculations regarding the nature of the causation of the disease it is evident that most of the older authors recognized that influenza was quite independent of general atmospheric or telluric conditions of season, climate, site, etc., as shown by the writings of Salius Diversus (1536), Molineux (1693), and others. This independence has been proved in a high degree by our latest pandemic. In its hurricane course around the world it affected all latitudes and longitudes, all zones, having traversed all points of the compass from the northern polar circle to the equator; at one time in the hottest season, as in eastern central Africa, upon the Zambesi and Shire, upon the Antilles and in the valley of the Indus; at another in the coldest season, as in Siberia and Greenland. The disease occurred in dry climates and seasons, as in northern Africa, Arabia, central Asia, and central Australia, while it flourished just as well as in the wet, tropical rainy season, e. g., in India at the time of the southwest monsoon. In the same way it was independent of altitude, occurring upon the sea coast as well as on the highest mountains. The disease was quite independent of wind and weather.
The weather reports of the meteorologic stations were studied with great industry in our latest pandemic. It was shown that during the epidemic of 1889 almost everywhere in Europe there were relatively high humidity, slight rainfall, and comparatively high temperature of the air. But it is in the highest degree unlikely that these meteorologic conditions had any influence on the rise and spread of influenza, or that they had the slightest influence upon the vitality of the free germs, or favored the public predisposition, yet upon these meteorologic conditions Assmann, Strahler, Ucke, Teissier, have formulated quite untenable theories.
Finally, as regards the influence of direction of the wind, the mode of distribution of influenza, quite apart from the meteorologic tables, shows the untenability of the general opinion that influenza was disseminated and carried by the wind from Russia. The prevailing wind was for the most part in a direction opposite to the course of influenza. No question has been more discussed by the historians of influenza than the mysterious direction of so many of the pandemics from east to west. The simple solution that this direction of the course of epidemics is the same as the direction of commerce between Russia, the home of influenza, and Europe, was not fully realized until our own time. If civilized states with similar commercial intercourse had existed east of Russia, influenza in 1889 would have traveled with the same rapidity in the direction from west to east as it did from east to west.
But although the pandemics in their storm like course around the world were independent of wind and weather, climate and season, it would, nevertheless, be a great mistake-and this mistake has generally been made even up to the present clay-were we to conclude that the origin of the primary pandemics and the local epidemics which followed were entirely independent of season (see p. 552). The facts are as follows: 1. Nearly all the numerous pandemics which at various times have had their origin in Russia arose there in the late autumn or in the winter months. 2. The latest pandemic (1889) and the succeeding severe epidemics in Europe and North America, in the years 1891-1894, occurred almost exclusively in the cold season, the summer remaining conspicuously free.
The spread of the pandemic over the earth is entirely independent of all atmospheric or telluric conditions, and is exclusively the result of contagion. The origin of the primary epidemics and of the after epidemics, however, is evidently dependent upon season.
A. Hirsch examined 125 independent epidemics or pandemics in reference to the influence of season, and found that 50 occurred in winter (December to February), 35 in spring (March to May), 16 in summer (June to August), and 24 in autumn (September to November). The conditions which make influenza dependent upon season cannot at present be defined. We must recognize that beyond the specific germ and its communicability by way of contagion, there are many conditions of whose influence we are still quite ignorant.