SOIL. 391 



crobes, the hay -bacillus, the potato-bacillus, and the root- 

 bacillus (p. 404) are cultivated from earth with great fre- 

 quency. Upon the bacteria of earth devolves the function of 

 disintegrating dead organic substances, and converting them 

 into materials from which new organic substances (plants) 

 are formed. The carbon of organic substances is trans- 

 formed into carbon dioxid ; the nitrogen, into ammonia ; and 

 the hydrogen, into water. Certain bacteria of the earth oxi- 

 dize the ammonia into nitrites (ferments nitreux, nitroso-bac- 

 teria) ; others, the nitrites into nitrates (ferments nitriques, 

 nitro-bacteria) ; the entire procedure of the transformation 

 of organic nitrogen into nitric acid is designated nitrification. 

 This transformation-process, which is brought about by the 

 bacterial flora of the earth, is absolutely indispensable to 

 the vegetable world. If plants are placed in soil that con- 

 tains all necessary nutritive elements, but has been sterilized 

 artificially that is, rendered bacteria-free they will de- 

 velop but incompletely, and soon begin to die (Duclaux). 

 It must be pointed out that these nitrifying bacteria develop 

 also in cultures that contain no trace of organic carbon- 

 compounds, and that they, therefore, obtain their carbon- 

 requirement directly from the carbon dioxid, without the 

 aid of chlorophyl and light. 



In the superficial layers of the earth, in addition to the 

 bacilli, many permanent spores are present, which in part 

 possess extraordinary resistance, and withstand for four or 

 five hours the action of live steam. Favorable conditions 

 for spore-formation must, therefore, be present in the super- 

 ficial layers of the soil. Perhaps the circumstance is of 

 significance that the individual particles of earth are sur- 

 rounded by a capillary zone of fluid, and are thus protected 

 from drying. It has been shown that anthrax-bacilli in 

 cultures mixed with porous particles of earth undergo 

 sporulation much more quickly and actively than otherwise. 

 Anthrax-spores retain their irifectivity for years in earth in; 

 which dissected animal carcases have been buried. Of 

 pathogenic bacteria, cultivated and manured earth fre- 

 quently contains, besides, the bacillus of tetanus and that of 

 malignant edema. 



The malarial parasites, likewise, must reside in the earth 

 in certain localities ; at least, numerous clinical facts support 

 such a view. Their demonstration therein has, however, 

 as yet not been successful. Other infectious agents have 



