BACTERIA IN NATURE IS 



the animal world is not sufficient to meet the demands of 

 the ehlorophyl plants, the importance of the part played by 

 bacteria in preparing food that can be assimilated by higher 

 plants can not be overestimated. The continuance on the 

 earth of the higher forms of life is, when reduced to its last 

 analysis, dependent upon the activities of microscopic organ- 

 isms. In addition to the preparation of organic matter for 

 plant food by the saprophytic bacteria, there are other spe- 

 cies which live in the soil and in the roots of certain legu- 

 minous plants that are able to take the free nitrogen from 

 the air and store it up in the roots of plants for their nour- 

 ishment.* 



In their work as scavengers, bacteria are undoubtedly 

 more or less assisted by other low forms of vegetation, such 

 as yeasts, moulds and possibly other fungi. The part, if 

 any, played by minute forms of animal life is not clearly 

 defined. 



Divisions of Bacteriology. When the study of bac- 

 teria is considered in a broad sense, bacteriology divides 

 itself very naturally into several quite distinct lines. 



1. The study of the bacteria in the soil and their rela- 

 tions to plant life constitutes what is now recognized as agri- 

 cultural bacteriology. 



* There are in nature, according to Fischer, five sources of nitro- 

 gen open to plants and animals: 



"1. The atmosphere (79 per cent, by volume of free nitrogen). 



2. The nitrates of the soil and the traces of nitrous acid formed 

 in the air during thunderstorms. 



3. Ammonia, which occurs in minuie quantities in the air, and 

 is set free abundantly by the putrefaction and decay of dead organ- 

 isms. 



4. Animal excreta, which contain nitrogen compounds of many 

 kinds, even down to ammonia; and 



5. The tissues of plants and animals. 



The first three of the above-named sources are useless to ani- 

 mals, for they obtain their nitrogen from plants only, either directly 

 (herbivora), or indirectly through other animals (carnivora). To 

 plants, on the other hand, n'trogen seemed until comparatively re- 

 cently to be available only in one of these three forms. Vegetable 



