THE STORY OF THE BACTERIA. 45 



but can remain alive for long periods fast 

 frozen in a mass of ice. Now a very curious 

 thing has been noticed in the ice which is 

 gathered in these regions and which we use 

 for domestic purposes, and that is, that the so- 

 called bubbly streaks which we usually see in 

 our ice blocks contain, as a rule, many more 

 bacteria than does the transparent ice close by. 

 It has been found, on cultivating the bac- 

 teria from the bubbly streaks, that the species 

 which was most abundant here is an oxygen 

 lover, and is also very mobile. Now the bub- 

 bles which collect in streaks or layers in the 

 ice collect during the daytime, or when the ice 

 is not freezing very fast below, and there is 

 time for the a$r-seeking bacteria to gather 

 around them in great numbers. But now, 

 when a clear night or a cold snap comes on, 

 the ice closes around both bubbles and bacte- 

 ria, and we have formed, to use the language 

 of the geologist, an air and fossil-bearing 

 stratum. Only our bacterial fossils are not 

 dead, and all we have to do in order to find 

 out what forms of life were present in our suc- 

 cessive geological periods, limited perhaps 



