THE MICROBIOLOGY OF THE ATMOSPHERE 



of 24 hours we inhale perhaps 50 micrograms of a mixture of microbes. 

 Ahhough some constituents of this mixture are harmful to allergic 

 subjects, this dose might also bring in useful quantities of active organic 

 compounds. Chauvin & Lavie (1956) found antibiotics in Salix and maize 

 pollen, and their presence in fungus spores, too, would not be surprising 

 {see Whinfield, 1947). We may wonder whether the reputed beneficial 

 effects of country air for human health are attributable not only to its 

 freedom from smoke and fumes, but also to positive gains from the air- 

 spora. 



Finally, to balance loss with gain, as the Earth's surface is the ultimate 

 receptacle of almost all spores liberated, it can be estimated that the soil 

 must receive a dose of fertilizer from the air-spora equivalent to perhaps 

 2 kg. of nitrogen per acre per annum — an amount that is negligible on 

 fertile land, but enough to aid plants colonizing barren places. 



130 



