DEPOSITION IN RAIN, SNOW, AND HAIL 



bacterial and mould colonies. The largest catches of bacteria occurred In 

 the warmer months, when numbers varied from o-ooo8 to 8-3 per ml., 

 with a general mean of 4-3 per ml., but these figures excluded the first 

 rain after several dry days when 200 bacteria per ml. might be recorded. 



During prolonged rainfall the numbers fluctuated instead of contin- 

 uing to diminish, suggesting to Miquel that the rain clouds themselves 

 had a characteristic bacterial content, with the percentage composition of: 

 Micrococcus (60), Bacillus (25), and Bacterium (15). Moulds fluctuated 

 in the same manner as bacteria and averaged 4 per ml. Miquel estimated 

 the annual precipitation of bacteria and moulds at Montsouris at over 

 4 million per square metre — a figure that was obviously too low as he 

 excluded the contribution of the first rain after dry days. 



The pharmaceutical use of rain-water induced Lindner (1899), 

 in Germany, to collect 28 samples of rain in a clean porcelain dish on a 

 bleaching ground near his house. Samples were then added to sterile 

 hay-infusions, albumen, milk, or blood serum. His liquid cultures gave 

 a regular succession of bacteria, flagellates, and monads, in the first 

 day or two and, later on, stalked Vorticella-like ciliates, Paramaecium, 

 Stylonychia, and Volvox. Once he got two amoeboid forms, but never 

 gregarines or coccidiens. Lack of precautions against splash-contamina- 

 tion appears to leave the interpretation of his data in doubt. 



In this century various workers have cultured microbes from rain. 

 Minervini (1900) collected numerous rain samples on board ship in the 

 North Atlantic. Bacteria were abundant, half the samples yielded pink 

 yeasts, and a quarter of them Penicillium. He also obtained Aspergillus 

 glaucus, A. niger, Monilia Candida^ and many other moulds. Busse (1926) 

 recorded pine pollen in rain. 



Rain-water collected over the ocean at considerable distances off" shore 

 by ZoBell (1946, p. 179) averaged i to 10 bacteria per ml, with few or no 

 mould fungi. Rain-water collected on land at the Scripps Institution of 

 Oceanography, California, contained from 10 to 150 microbes per ml. 

 As usual, the highest counts were obtained during the first rain and were 

 associated with a predominance of mould spores. 



Protozoa in rain were studied at Heidelberg by Puschkarew (1913), 

 who collected ten samples of rain-water in a sterile funnel, and added 

 nutrient solutions. At the start of rain he found large numbers of fungi 

 and bacteria, and the numerous protozoa included a new species. 

 Amoeba polyphagus^ with species of Bodo^ Manas, Calpoda, and other 

 genera. 



Twice in the month of November, rain was collected in sterile flasks 

 on a roof at Leiden by Overeem (1937) and inoculated into flasks of a 

 nutrient medium favourable to growth of green plants in light. In a total 

 of 221 cc. of rain-water she obtained the following cultures. Algae: 

 Stichococcus minor (8), S. bacillaris (5), Chlorococcum sp. (7), Pleurococcus 

 vulgaris (4), Chlorella vulgaris (2), Hormidium flaccidum (2), and Navicula 



149 



