3 8 THE POPULAR SCIENCE MONTHLY. 



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 in- 

 validate 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, espe- 

 cially those of hospitals, proceeding from substances in a state of putre- 

 faction, sanious pus, and the dejections of the sick, are charged w T ith 

 microbes. Great agglomerations of men furnish the most of them. 

 According to the measurements made in the Rue de Rivoli and Mont- 

 souris, 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 Asnieres, 

 48,000 ; rain-water, 64,000 ; water of the Vanne (Montrouge basin), 

 248,000 ; water from the Seine (drawn at Bercy), 4,800,000 ; w r ater 

 from the Seine (drawn at Asnieres), 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 mul- 

 tiplication 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 con- 

 tinuation of the statistical researches that have been begun at Mont- 

 souris, 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 



