1889.] Bacteriology. 167 
a snow storm, in a sterilized tube. The snow so taken was 
melted in a water bath at 30° C. and.sC.C. of this melted 
snow mixed with nutrient-gelatin. From this, plates were 
prepared in the usual way. Other samples of the same snow 
were also planted, and an average of these showed pretty 
well how many bacteria were ordinarily contained in such 
To insure as exact results as possible, two samples of snow 
and as free from 
:ers as possible. 
From fresh, fallii _ 
tained:— 
Feb, 2, 1888. Average temperature, — 7.2^ C. 
In the first sample 34 bacteria to i c.c. of melted snow. 
In the second, 38. 
Feb., 21, 1888. Average temperature — ii.i^C 
In the first portion, 203. 
In the second, 384. 
Feb., 28, 1888. Average temperature — 12.2 
In the first portion, 140. 
In the second, 165. 
Although these figures differ widely they nevertheless teach 
us something of the bacteriology of snow, and do not show 
wider differences than different examinations of ice, made by 
Frankel, Prudden and others. A part of the bacteria found in 
snow arecontained in the vapor when it crystallizes. Another, 
and the larger part, are filtered from the air by the cottony 
snow-flakes in falling. Consequently, the number of bacteria 
in the air must be much diminished, after a snow fall, and a true 
cleansing of the atmosphere appears to be accomplished, such 
as takes place during a rain. It is also clear that the cottony or 
wooly structure of the snow-crystal aids in producing this 
effect, in no small degree. Large differences sometimes 
noticed in like portions, might be due to the fact that during 
a snow storm, the snow may sometimes become mixed with 
impurities gathered from buildings in the vicinity, etc. 
In studying snow which has been lying for some time 
Janowski took samples from the upper layers of snow which 
had fallen several days before, and which had since lain 
exposed to the air. In considering the results, it is import- 
ant to know the range of temperature to which the snow was 
exposed. This was learned from the official weather reports 
at Kiew, where his investigations were made. 
By means of a sterilized plate of glass he then removed the 
top of the snow, half a centimetre deep, on top of which the 
dust from the air rested. From the layer thus uncovered he- 
took his samples and prepared plates as before. 
