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THE POPULAR SCIENCE MONTHLY 



As M. Miquel remarks, the use of aeroscopes will be of value for the 

 discovery in the air of the germs of the molds which attack our cere- 

 als. Regarding the etiology of certain contagious affections, he con- 

 tinues : " It does not seem to be proved that the various spores in- 

 troduced into our economy, to the number of 300,000 a day, or 

 100,000,000 a year, are perfectly innocuous. The appearance of thrush 

 in the mouths of young children and in the respiratory canals of the 

 dying seems to demonstrate also that the molds form a part of the 

 class of parasites which are ready to take possession of our organism 

 whenever it presents a vulnerable point or a point of weak resisting 

 power." 



M. Pasteur has long insisted on the utility of these researches. 

 " I believe," he wrote in 1862, " that it would be of great advantage 

 to multiply the studies on this subject, and to compare in the same 

 place at different seasons, and in different places at the same time, the 

 number of corjmscles disseminated in the atmosphere. Our knowl- 

 edge of the phenomena of morbid contagion, especially during the 

 jDrevalence of epidemics, would, it appears to me, gain from researches 

 prosecuted in this direction." 



Since M. Pasteur has established the parasitic character of zymotic 

 diseases like the hen-cholera, sheep-rot, septicaemia, measles, etc., the 

 rnicrographic statistics of the air has risen to a considerable impor- 

 tance. It has had, however, to concentrate its efforts chiefly upon a 

 class of rudimentary organisms very different from the green algae 

 and the molds of which we have spoken. This group is the one to 

 which the viruses belong. The plants composing it, and which are 

 designated under the common denomination of bacteria, escape the 

 process of numeration in use for the higher cryptogams. In conse- 

 quence of their extreme minuteness and refractive power, they are 



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Fio. 4. Specimens of bacteria. A, Micrococcus in isolated cells or aggregated into balls and 

 strings; B, Bacterium ; C. Bacillus; a, batonnets (adult bacilli i; b, batonncts with spore6 ; 

 c, isolated spores ; d, germinating spores. 



invisible, and unrecognizable in the preparations of the aeroscopes. 

 Their existence in the air was long denied, and the proof that they 

 abound in it only dates from the experiments that were instituted by 

 M. Pasteur for the solution of the question of heterogeny. The meth- 



