364 MICROBIOLOGY OF SOIL 



forming soils of Tortugas Island, indicating the universal occurrence 

 of these organisms in the soil. Many species of actinomycetes have 

 been demonstrated to occur in the soil to the extent of millions of cells 

 per gram. As to the activities of Actinomyces in the soil, Beyer- 

 inck has shown that the Act. chromogenus produces an oxidizing sub- 

 stance, quinon (C 6 H 4 O 2 ) which may play an important part in the 

 oxidation of organic matter in the soil. Munter, Krainsky and Scales 

 have demonstrated that many Actinomyces are able to decompose cellu- 

 lose in the soil, and that in some instances this ability is very marked. 

 Krainsky records that soil Actinomyces need very little .nitrogen for 

 their life activities, and that they can get it from any available source. 

 If nitrates are present, these are reduced first to nitrites, and then 

 utilized. Waksman and Curtis, working with soil sterilized by steam, 

 did not find any great accumulation of ammonia through the activities 

 of Actinomyces, although different species seemed to show marked varia- 

 tion in their power to accumulate ammonia. 



ALG.&. At times the influence of algas in changing the character of 

 the soil as a culture medium for bacteria is quite considerable. As 

 chlorophyll-bearing organisms they are enabled to manufacture sugar 

 and starch with the aid of sunlight, and to favor thus the development 

 of Azotobacter and of other microorganisms dependent for their energy 

 on the organic matter in the soil. Investigators both in France and 

 in Germany have found that the fixation of nitrogen in sand used for 

 pot culture experiments occurs in the surface layer possessing a growth 

 of alga?. The advocates of bare fallows attribute the greater pro- 

 ductivity of fallowed land to the growth of algae, the accumulation of 

 nitrogen through their influence and to other changes affecting the soil 

 bacteria. 



PROTOZOA. It has been known for a long time that certain species 

 of protozoa are common in soils and that their food consists of bacteria. 

 To what extent protozoa play a part in soil fertility has not yet 

 been fully explained, even though Russell and Hutchinson of the 

 Rothamsted Experiment 'Station have maintained that these minute 

 animals are extremely important in that they maintain a certain bac- 

 terial equilibrium in the soil. Their claim is mainly based on the fact 

 that partially sterilized soils (either by means of heat or antiseptics) 

 soon come to contain enormous numbers of bacteria, 



It is, therefore, assumed by them that this abnormal increase is 



