THE MICROBIOLOGY OF THE ATMOSPHERE 



were predominantly cocci and spore-formers (though in a local flight 

 over Churchill gram-positive pleomorphic rods predominated). Fungi 

 were mainly Cladosporium and Alternaria, but included Penicillium^ 

 Papularia^ and Stemphylium. 



In the summer of 1950, northern air was sampled daily by McGill 

 workers for 21 days with the G.E. Electrostatic sampler and the slit 

 sampler on a roof 17 metres above ground at Churchill near the tree-line 

 on Hudson Bay. This survey formed the standard of reference for two 

 flights to Resolute Bay, Cornwallis Island, some 1,600 km. to the north, 

 on 1-3 August 1950, at an altitude of around 3,000 metres. At Churchill 

 the catch consisted of: gram-positive pleomorphic rods (46 per cent), 

 gram-negative rods (20 per cent), spore-forming rods (18 per cent), and 

 cocci (15 per cent). In the two flights to Resolute Bay in the Arctic during 

 this period, 51 per cent of the bacteria caught were spore-forming rods 

 (Pady & Kelly, 1953). Fungi were assessed both in culture, and visually 

 on silicone-coated slides: the numbers per cubic metre, with the visual 

 counts in parenthesis, were: Cladosporium, 17 (132), with its maximum 

 in an air mass of tropical origin; Alternaria, 0-7 (2-1); Stemphylium, i-i 

 (i-8); rusts (9-2); smuts (Ustilago) (86); yeasts, 3-5 (304); and Penicillium, 

 2-1. Of the fungus cultures, 57 per cent were non-sporulating. In addition, 

 Fusarium was reported as common on slides but rare in culture, and 

 Septoria was sometimes abundant on slides. An interesting list of fungi 

 which were caught only infrequently includes: Pullularia, Actinomycetes, 

 Botrytis, Aspergillus, Verticillium, several ascomycetes, and a single culture 

 of Cunninghamella — one of the rare isolations of a mucoraceous fungus 

 from the upper air. In addition there were numerous moss spores and pollen 

 grains, which together averaged 20 per cubic metre (Pady & Kapica, 1953). 



On the flights to Resolute Bay at 3,000 metres, the fungi were 

 essentially the same as at ground-level at Churchill; but they were in 

 much lower concentrations averaging 12 per cubic metre (125 per cubic 

 metre if determined visually) and were principally yeasts, Cladosporium, 

 and Ustilago. Pollen grains averaged 16 per cubic metre; and in warm air 

 on the southern part of the flight moss spores averaged 47 per cubic 

 metre. It was thought that the southern parts of these flights lay through 

 an old continental tropical air mass, which had moved into the Arctic 

 where most of the spores had died; north of this was cold polar air 

 containing very few spores. The general conclusion reached was that 

 the air-spora over the Arctic comes mainly from the agricultural regions 

 of the south (Pady & Kelly 1953; Pady & Kapica, 1953). However, the 

 larger numbers caught at ground-level at Churchill, and the numerous 

 moss spores, suggest that the tundra also made an important contribution. 



MICROBIOLOGY OF AIR MASSES OVER NORTHERN CANADA 



The earlier McGill studies suggested that, in the upper air above the 

 level of pronounced concentration gradients, microbial concentration 



142 



