MICROSCOPIC LIFE IN THE AIR. 



37 



the only means of discovering the nature of the organisms, for char- 

 acteristics deduced from their shape are of no significance. Most fre- 

 quently they can he distinguished only by the fermentations they 

 produce. Numerous experiments based on this principle will be re- 

 quired for the exact determination of the bacteria in the atmosphere. 

 In the present condition of the science, we have to limit ourselves to 

 the general statistics of the Micrococci, Vibrios, Bacteria, Bacilli, 

 and Cladothrices that live in the air, without undertaking to classify 

 in any precise way all the beings comprehended under each of these 

 denominations. 



The observations conducted at the Observatory of Montsouris show 

 that there are on the average eighty bacteria in a cubic metre of air. 

 The highest number was observed in the fall, the lowest in the winter. 

 There were found fifty bacteria in December and January, only thirty- 

 three in February, one hundred and five in May, fifty in June, and one 

 hundred and seventy in October. The diagrams of daily observations 



N 124 



IMW 108 



^PA'R I 5 | 



Jr NE 152 



W 77 



E 130 



SW 58 



SE 74 



S 42 



Fig. 8. Influence of the Direction of the Wind on the Number of Aerial Microbes 



collected at montsouris. 



show that the number of spores of these alga? increases with the tem- 

 perature. Inversely to what takes place in the case of the molds, the 

 number of the schizophytes, small in rainy weather, rises when all the 

 moisture has disappeared from the surface of the soil. The counter- 

 action of moisture is stronger than the direct action of temperature ; 

 and this fact accounts for the rarity of the bacteria after the great 

 rains of February, April, and June. Still a long period of dry weather 

 does not appear to be favorable to the development of the plants. 



