Remarkably interesting results are revealed by comparing the course of the epidemic of the spring of 1833 through the Prussian garrisons with the corresponding behavior of the pandemic of 1889-90. In the year 1833 the pestilence, conformably with the means of communication at that time, progressed not only very slowly, but also in an accurate geographic direction from east to west. On the other hand, in the pandemic of 1889-90, a geographic course is hardly recognizable. The sequence in which the Prussian garrisons were attacked is no longer determined by their geographic location, but chiefly by their position as trade centers. The progress of the disease in 1833 was as follows:
March 4, Garrison Memel; March 13, Tilsit, Insterburg; March 17, Konigsberg; March 23, Gleiwitz; March 25, Posen; April 8, Magdeburg; April 20, Erfurt; May 1, Minden; May 15, Mainz; beginning of June, Cologne, Coblenz, Aix la-Chapelle; June 10, Luxemburg.
It, therefore, required three months for the epidemic to progress from the garrison at the extreme east to that at the extreme west. In the year 1889-90 the difference in time between the garrisons was at the most five weeks.
But the order of attack was entirely different in 1889-90. From the end of November to December 6: Berlin, Thorn, Kiel, Stettin, Dantzig; December 7 to 10: Breslau, Dresden, Munich, Potsdam, Halle, Mainz, Strassburg (very likely infected from Paris), Spandau; December 11 to 15: Posen (!), Graudenz, Ulm,Cassel, Darmstadt, Magdeburg, Hannover, Minden, Cologne; December 16 to 20: Leipsic, Wiirzburg, Stuttgart, Giessen, Hamburg, Konigsberg (!); December 21 to 31: Neisse, Riosa, Chemnitz, Zittau, Nuremberg, Ratisbon, Muhlhausen i. E., Karlsruhe, Colmar, Coblenz, Bonn, Minister, Wesel, Diisseldorf, Altona, Schleswig, Gumbinnen, and Insterburg (!). In January: Inowrazlaw (!), Glatz (!), Wiblingen, Lindau, Diedenhofen, Stolp.
In commending this compilation to the reader for closer study we would only add that the German garrisons which remained exempt from the disease were almost all in places like Burg, Bojanowo, Samter, Schrimm, Bernstadt, Parchim, and Roffwein, hardly known to the non military German even by name.
The fact that in some garrisons the military remained exempt from influenza (Liegnitz, Beuthen, Aurich) while the civilians were severely affected is an occurrence which requires separate investigation (compare p. 571). Occasionally, in earlier times, influenza traveled very rapidly. In 1782 it progressed from Leipsic to Amsterdam in eighteen days, being brought by Dutch merchants returning from the Leipsic fair in this short time to their native country.
The direction and the road that pandemic influenza follows whenever it spreads over countries and hemispheres, as also when it is restricted to a particular locality, province, or district, are exclusively determined by intercommunication.
The main cities, the capital, and the commercial centers are generally affected sooner than the smaller places; the latter again sooner than the villages and lowlands and the distant mountains.
Isolated districts upon the Russian frontier, numerous purely country districts, the Thuringen and the Black Forests, the Bavarian Alps, the Bavarian woods (Cham, Regen), the higher Harz and Vos ges districts, etc., were reached by the disease much later than other sections.
The districts situated upon the railroad, as shown by numerous examples, are, as a rule, affected much earlier than those situated at some distance from the railroad.
When influenza is carried by ships, it is the coast and harbor cities of those parts of the world to which the ships are sailing where the disease will enter, and the time of infection of the interior portions of such countries will depend upon the rapidity of travel, as was observed especially in Australia, in Africa upon the Zambesi, in Ceylon, and in many other seaport towns.
Innumerable examples might be quoted to prove the above mentioned behavior of influenza, but at the same time there are many and noteworthy exceptions to the rule.
To quote but one example, it appears that Konigsberg, which is the entrance port to Russian commerce, was attacked considerably later than Berlin, Paris, and many of the cities in the extreme west of Germany.
Accident plays so large a part in the spread of contagious diseases that occasionally small districts, hamlets, villages, and isolated farms may be affected by influenza sooner than large cities in their immediate neighborhood. Numerous proofs might be adduced to substantiate this. The Bavarian report shows that the large cities of Munich, Nuremberg, Wiirzburg, Augsburg, and Ratisbon were affected later than the smaller rural places. A simultaneous affection of both city and country is occasionally noted. In densely populated districts the rapidity with which the disease spread in town and country was so great that a difference of date of infection could not be observed. In sparsely populated districts with widely distant villages influenza required more time to spread over a small area than it did to spread over the main cities of Europe and over the ocean.
As an example, the behavior of influenza in the province of Schleswig-Holstein may serve. The capital, Kiel, was one of the first districts in Germany to be affected, and yet influenza required fully two months to spread itself to the more distant and isolated districts of the province.
In the purely rural districts of Salford (England), influenza required a period of four months (December to March) to spread; while in the industrial cities a few weeks were sufficient.
Numerous remarkable exceptions to this rule have been noted in literature also, but we need only allude to the rapid spread of the disease among the almost isolated and widely separated farm houses in the district of Bradwell-" the strongest piece of evidence of the atmospheric origin," as the author thinks.
Attention must also be drawn to the exceptionally slow spread of the epidemic in England. Is it not remarkable that although London was infected on December 11, cities of the magnitude of Birmingham, Manchester, Glasgow, Sheffield, Liverpool, Edinburgh, and others were first affected toward the end of December or the beginning of January?