The number rises at first during the hot season, but diminishes under the influence of a progressive desiccation toward the second or third week.
The diminution in hygrometric conditions manifested in September and October explains the recrudescence of the bacteria during these months. Some micrographers have suggested that the germs may be transported by the vapor of water; but M. Miquel's experiments invalidate this hypothesis, and indicate that the evaporation of water from the surface of the ground never carries any schizophytes with it. On the other hand, numerous tests have shown that dry dusts, especially those of hospitals, proceeding from substances in a state of putrefaction, sanious pus, and the dejections of the sick, are charged with microbes. Great agglomerations of men furnish the most of them. According to the measurements made in the Rue de Rivoli and Montsouris, the air in the interior of Paris is nine or ten times richer in bacteria than that in the neighborhood of the fortifications. At the observatory, the winds from the north bring many more than the winds from the south.
The vertical distribution of the microbes also shows that they come mostly from the dirt of our streets and houses. While a cubic metre of air at the top of the Pantheon contains only twenty-eight of them, the same quantity of air in the Park of Montsouris contains forty-five, and in the mairie of the fourth arrondissement, four hundred and sixty-two. These numbers are, however, insignificant in comparison with those furnished by the analyses of sewer-waters. We give a few specimens from M. Miquel's analyses, in which is shown the number of microbes found in a litre of water from each of the sources named: Condensed atmospheric vapor, 900; water from the drain of Asnières, 48,000; rain-water, 64,000; water of the Vanne (Montrouge basin), 248,000; water from the Seine (drawn at Bercy), 4,800,000; water from the Seine (drawn at Asnières), 12,800,000; sewer-water (drawn at Clichy), 80,000,000. These figures represent the minima. Left to stagnate, sewer-water putrefies in a very short time, through the multiplication of its germs, and the microbes become a thousand times as numerous as indicated in the summary.
Thus, we see, we are surrounded on every side by myriads of schizophytes. What proportion, among these minute inhabitants of the atmosphere and the waters, have a part in producing contagious maladies and the epidemics by which the populations of our large cities have been decimated at times? We do not know yet. The continuation of the statistical researches that have been begun at Montsouris, and the microscopic analysis of the air and of water, particularly of sewer-water, cultivation, botanical and physiological investigation, and inoculation with the resultant germs, will certainly conduct to the solution of the problem. Then only, having become acquainted with our enemies, shall we be able to destroy them. The precautions that
