84 MICRO-ORGANISMS IN WATER 



under investigation. Since these results were published 

 a very large number of researches have been undertaken 

 to obtain, by means of the modern methods of inves- 

 tigation, more precise information as to the bacterial 

 ■contents of water, and the conditions under which 

 micro-organisms not only gain access to, but exist in, 

 various waters. 



Snoio. — Some interesting experiments on the bacte- 

 rial contents of snow have been carried out in Eussia 

 by Janowski.^ In the first place snow which had been 

 lying for some time was examined ; the superficial 

 layers were removed and the sample taken from below, 

 so as to ensure the absence of any disturbance through 

 aerial contamination. The snow was allowed to melt in 

 a test-tube, and plates were poured with the following 

 results : — 



1. On February 11, no snow having fallen on the 

 previous day, 1 c.c. of snow-water yielded 3 organisms 

 (mean of two experiments). 



2. On February 15, no snow for 4 days, 10 per 

 c.c. (mean of two experiments). 



3. On February 24, no snow for 3 days, hard frost, 

 228 per c.c. 



4. On March 2, no snow for 3 days, 178 per c.c. 

 (mean of two experiments). 



Thus, in spite of prolonged exposure to a low tem- 

 perature, e.g,^ after three days during which the ther- 

 mometer only reached —16° C. in the middle of the day 

 on February 24, the snow contained a considerable 

 number of micro-organisms. Janowski also examined 

 freshly fallen snow, and found varying numbers per 

 c.c. In samples collected at a temperature of about 

 — 7'2° C. in the month of February he found from 34 to 



^ * Ueber den Bakteriengehalt dee Schnees,' Centralhlatt filr Bak- 

 teriologie, vol. iv., 1888, p, 547. 



