38 THE STORY OF GERM LIFE. 



or not. This method avoids the giving of separate 

 names to the same species found by different 

 observers, and it is hoped that gradually accumu- 

 lating knowledge will in time group together the 

 forms which are really identical, but which have 

 been described by different observers. 



WHERE BACTERIA ARE FOUND. 



There are no other plants or animals so uni- 

 versally found in Nature as the bacteria. It is 

 this universal presence, together with their great 

 powers of multiplication, which renders them of 

 so much importance in Nature. They exist almost 

 everywhere on the surface of the earth. They 

 are in the soil, especially at its surface. They do 

 not extend to very great depths of soil, however, 

 few existing below four feet of soil. At the sur- 

 face they are very abundant, especially if the soil 

 is moist and full of organic material. The num- 

 ber may range from a few hundred to one hun- 

 dred millions per gramme.* The soil bacteria 

 vary also in species, some twoscore different spe- 

 cies having been described as common in soil. 

 They are in all bodies of water, both at the 

 surface and below it. They are found at con- 

 siderable depths in the ocean. All bodies of fresh 

 water contain them, and all sediments in such 

 bodies of water are filled with bacteria. They 

 are in streams of running water in even greater 

 quantity than in standing water. This is simply 

 because running streams are being constantly 

 supplied with water which has been washing the 

 surface of the country and thus carrying off all 



* One gramme is fifteen grains. 



