MICROSCOPIC LIFE IN THE AIR. 



29 



with glycerine, and placed at the bottom of the cylinder, receives the 

 jet of air which is produced by the aspirator. The glycerine retains 

 the corpuscles which are brought in by the current, and it is then easy 

 to observe them. This apparatus has been modified in various ways, 





Fig. 1. Pouchet's Aeroscope. 



but with it, or something like it, the earlier investigators, MM. Pasteur, 

 F. Pouchet, Maddox, Douglas Cunningham, and others, have explored 

 the atmosphere. It did not take long to discover that the air around 

 us contains remnants of articles that we use existing in the condition 

 of impalpable dust. Wool from our clothing, cotton, silk, starch, are 

 floating in it, associated with fragments of various kinds butterflies' 

 scales, dried tarsuses of insects, feather-barbs, and skeletons of little 

 worms. Pollens of the coniferre and of numerous plants are abundant 

 in it during the floral season. Particles of mineral matter are also 

 found there, among them those curious spherules of meteoric air which 

 have been described by M. Gaston Tissandier.* 



Attention is, however, most strongly fixed upon the number and 

 variety of spores of cryptogams of which the air operates as a vehicle 

 of dissemination. Germs of the common molds, and the reproductive 

 cells of the algae that live on the roofs of houses, on walls, and on 

 damp earth, are nearly always abundant. M. Miquel has tried to de- 

 termine the laws that govern the appearance of these plants in the 

 atmosphere. He first counted them, by disposing his aeroscopes so 

 that they should register the volume of the air passing through them, 



* See " Popular Science Monthly," July, 1880, article " Atmospheric Dust." 



