164 MICROBES, FERMENTS, AND MOULDS. 



two or three days of damp, rainy weather, the rain- 

 water often contains more bacteria than when it began 

 to fall. Since the atmosphere is then excessively pure, 

 it seems that the bacteria are able to live and 

 multiply in the clouds, or else that the clouds, in 

 their passage through space, take up a varying con- 

 tingent of germs." 



The maximum of air-germs is observed in autumn, 

 the minimum in winter; thus, 50 bacteria were counted 

 in December and January, only 33 in February, 105 

 in May, 50 in June, and 170 in October. 



Inversely to what occurs with moulds, the number 

 of bacteria, low in rainy weather, rises when all 

 moisture has disappeared from the surface of the soil. 

 The effect of dryness is greater than that of warmth. 

 This explains the scarcity of bacteria after the great 

 rains of February, April, and June. A long drought 

 is, however, unfavourable to their development. 



Miquel's experiments lead him to conclude that 

 dew, the evaporation from the soil, is never charged 

 with spores. The dry dust in the neighbourhood of 

 inhabited places, and especially of hospitals, is, on the 

 other hand, charged with microbes. In the centre of 

 Paris, for example, in the Rue de Rivoli, there are 

 nine or ten times as many microbes in the atmosphere 

 as in the neighbourhood of the fortifications. In the 

 Montsouris Observatory, south of Paris, the north 

 winds bring many more bacteria than the south winds. 

 The most impure wind comes from the hills of Villette 



