THE MICROBIOLOGY OF THE ATMOSPHERE 



with insecticides and fungicides has been claimed to spread some fungal 

 diseases. 



Marine Air 



The oceans, forming three-quarters of the Earth's surface, act as a 

 vast source, putting a mainly bacterial microbial population into the 

 atmosphere. Compared with air over land, the concentration in surface 

 layers over sea is usually very small. Processes by which marine organisms 

 become airborne include : spray droplets from the breaking of waves on 

 shore or at sea; foam blown off white-caps; and bursting of bubbles 

 produced by white-caps, rain or snow (Blanchard & Woodcock, 1957). 

 These processes, however, also facilitate removal of suspended particles 

 from sea-air by the large liquid surface whose relatively constant tem- 

 perature determines continued up-and-down movement in the lower 

 layers of air. 



Much of the older work is reviewed, and new data added, by ZoBell 

 (1946). A critical appraisal of the whole subject of aerobiology comes from 

 Jacobs (1951), who calculated, on the basis of salt-concentration of the 

 air and the bacterial concentration of sea water (which seldom exceeds 

 500 per cc), that the number of marine bacteria in air near the sea surface 

 averages about 5 per cubic metre. 



The microbial exploration of marine air was pioneered by Miquel 

 (1885, 1886) with the help of a sea captain, Mons. Moreau, during seven 

 voyages. For visual examination of crytogamic spores, an aspirator was 

 worked by suction provided by an engine condenser — an arrangement 

 which sampled 700 litres per 24 hours. Bacteria were estimated by drawing 

 air through glass-wool plugs in tubes at the rate 1,000 litres per 24 

 hours, washing the plugs, and inoculating aliquots into flasks of liquid 

 beef extract. A total of 113 cubic metres sampled in the seven voyages 

 averaged i bacterium per cubic metre, or o-6 per cubic metre if samples 

 taken within 100 km. of land were excluded. 



Visual counts over the ocean usually showed a few hundred cryto- 

 gamic spores and many pollen grains per cubic metre (i/30th of the 

 number usual on land), but on one occasion a total of 3,700 per cubic 

 metre were found at a distance of 30 km. from land in a wind off the coast 

 of Senegambia; this comprised a spora very different from that found by 

 Miquel in Paris. Near to continents the winds coming from land always 

 brought impure air, but the sea rapidly purified it and so a broad stretch 

 of water provides an effective obstacle to the spread of contagious epi- 

 demic diseases. In normal weather, bacteria from sea water were not put 

 into the air, but in rough weather Miquel found that the sea air contained 

 a few marine bacteria. 



The air in a ship's saloon always contained incomparably more 

 microbes than sea air, but its purity increased rapidly in the early days 

 of the voyage until it reached an equilibrium between purification by 



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