DEPOSITION IN RAIN, SNOW, AND HAIL 



basin : 'elaborate precautions having been taken to prevent contamination, 

 the thawed-out samples showed under a cover-slip cocci, motile bacilli, 

 and, invariably, zoogloea masses of bacteria in moderate numbers. 

 Diplococci, and occasionally cocci, were observed to be invested by a 

 pale capsule. ... A glucose agar slope culture of falling snow showed a 

 few small greyish colonies.' 



Atkinson isolated a motile bacterium believed to have been carried 

 to the Antarctic by upper-air currents and brought do\Mi by the snow 

 (Scott, 1913). Most of the arctic and antarctic snow samples were taken 

 from fallen snow, and organisms could therefore possibly have reached 

 the snow by a process of dry deposition (e.g. Salimovskaja-Rodina, 1936; 

 Darling & Siple, 1941) and are considered in Chapter IX. 



Hail 



Large numbers of microbes were recorded by Bujwid (1888), who 

 collected hailstones in Warsaw in the month of May, washed them in 

 sterile water, and, plating out the melt- water, found 21,000 bacteria per 

 ml. They included Bacillus fluorescens liquefackns, B.f. ptitridus, and 

 B. janthinus. From these numbers Bujwid concluded that surface waters 

 must have been carried aloft and frozen. 



During a hailstorm in St. Petersburg, windows were broken by hail- 

 stones the size of walnuts. Foutin (1889) washed some of these and, on 

 plating-out the melt-water, obtained 628-729 bacteria per ml., but no 

 fungi or yeasts. 



In July storms at Guelph, Ontario, Harrison (1898) collected hail- 

 stones, washed them in i in 500 mercuric chloride solution and, after 

 rinsing, plated-out the melt-water. One storm gave 955 colonies per stone, 

 of mixed bacteria and moulds, including ''Penicillhim glaucum\ Miicor 

 sp., Aspergillus sp.. Bacillus fluorescens liquefaciens^ B.f. non-liquefaciens, 

 and Proteus vulgaris. A later storm averaged 1,125 colonies per ml. but 

 these included fewer moulds than the first. Harrison concluded that the 

 bacteria must have come from surface water, but that the moulds were 

 picked up from the air. Belli (1901) obtained 140 organisms per ml. of 

 hail melt-water, of which eight were Aspergillus or Penicillium and the 

 remainder bacteria. Hail has also been sampled by Dubois (191 8). 



The organisms in precipitation water remain almost unstudied. The 

 little we know from existing records is tantalizing. Precipitation water is 

 non-sterile, whether on land, over the oceans, or about the poles. A wide 

 variety of organisms has been recovered from such waters — including 

 bacteria, fungi (moulds, yeasts, and plant pathogens), algae, liverworts, 

 mosses, pollens, and protozoa. Microbes are found in rain, hail, and snow, 

 when collected as it falls — before the possibility of ground contamination. 

 The highest counts are recorded from hail and, at present, these are 



153 



