190 POUCHET, OX ATMOSPHERIC MICROGRAPHY. 



extracted with care and examined under the microscope, there 

 will be found concentrated upon it, and on a surface of 

 extreme minuteness, all the corpuscles which float invisibly 

 in a volume of the atmosphere relatively immense, and which 

 can be accurately determined by calculation from the known 

 capacity of the aspirator. 



In order to give the apparatus still greater precision, and 

 to preclude the possible escape of any corpuscles, even among 

 the most minute and lightest, the glass disc may be covered 

 with some adhesive substance. By this means every particle, 

 without exception, will be attached to the surface at the very 

 spot to which the current of air conveys it. 



If it be preferred, the corpuscles may be disseminated upon 

 the glass disc, if the tube be terminated not by a single 

 minute orifice, but by a small flat diaphragm, perforated like 

 the rose of a watering-pot. 



On the other hand, whilst my aeroscope, as it may be 

 termed, clearly demonstrates that that abundance of germs of 

 which so much talk is made, but which has never been shown, 

 nowhere exists in the air : by a series of comparative expe- 

 riments in sowing the atmospheric corpuscles, under circum- 

 stances favorable to the development of the proto-organisms, 

 I have never seen that the soil thus sowed was more fecund 

 than that which had not. 



Nevertheless, if we were able, as is pretended, to sow 

 cryptogams or microzoa collected from the air by means of 

 balls of cotton, it is evident that every time these atmospheric 

 corpuscles were placed in suitable circumstances, a quantity 

 of proto-organisms would also be developed proportionate to 

 the amount of atmospheric detritus employed. But, I repeat, 

 experience has refuted all such pretensions. 



In similar vessels, under glass-bells of the same capacity, 

 at identically the same temperatures and degrees of pressure, 

 and in equal quantity, flour-paste, sowed with atmospheric 

 corpuscles, has never shown itself more fecund in orga- 

 nisms than that which had not undergone this preparation. 

 This sowing was very readily effected, either by the aid of a 

 fine muslin tamis, to disseminate the spores, if there had 

 been any; or simply by the exposing of the vessels in situ- 

 ations where the air had been agitated, in order to secure an 

 abundant deposit of its corpuscles. Vessels thus sowed, and 

 those carefully covei'ed over, were equally fertile. Further 

 than this, some Nile mud, heated for an hour to 160° C, and 

 reduced to powder, was not less prolific than that which had 

 not been submitted to that temperature. Nevertheless, ac- 

 cording to the opinion opposed to us, the contrary of what 

 we observed should have taken place. We have, moreover, 



