CONTENTS 



PART A. OCCURRENCE AND DIFFERENTIATION OF MICRO- 

 ORGANISMS IN THE SOIL 



Chapter I 



NUMBERS OF DIFFERENT GROUPS OF MICROORGANISMS FOUND IN THE SOIL AND 

 METHOD OF DETERMINATION 



The occurrence of microorganisms in the soil. Proof of microbial activities 

 in the soil. Methods of study. Direct microscopic method. Organisms 

 found in the soil by the direct microscopic method. Cultural methods for 

 demonstrating the kinds of organisms active in the soil. Cultural methods 

 for the determination of numbers of microorganisms in the soil. Culture 

 media. Sampling of soil. Treatment of soil samples and preparation of 

 plates. Incubation of plates and counting of organisms. Mathematical 

 interpretation of results. Comparison of plate and microscopic methods. 

 Numbers of bacteria in the soil. Bacterial numbers in manure. Numbers 

 of bacteria in the soil during different seasons of the year. Distribution 

 of bacteria at various depths. Numbers of specific physiological groups of 

 bacteria. Numbers of actinomyces in the soil. Numbers of fungi in the 

 soil. Methods of counting protozoa. Numbers of protozoa in the soil. .. . 3 



PART B. ISOLATION, IDENTIFICATION, AND CULTIVATION OF 

 SOIL MICROORGANISMS 



Chapter II 



PURE CULTURE STUDY AND CLASSIFICATION OF SOIL BACTERIA 



Pure culture study. Differentiating characters of bacteria. Life cycles of 

 bacteria. Classification of soil bacteria based upon their physiological 

 activities 53 



Chapter III 



AUTOTROPHIC BACTERIA 



The nature of autotrophic bacteria. Bacteria deriving their energy from 

 nitrogen compounds. Solid media for the isolation and cultivation of the 

 nitrite forming organisms. Morphology of the nitrite forming organisms. 

 Nitrate forming organisms (Nitrobacter). Occurrence of nitrifying bac- 

 teria in the soil. Bacteria deriving their energy from the oxidation of 

 sulfur and its compounds. Classification of sulfur bacteria. Oxidation of 

 selenium and its compounds. Bacteria oxidizing iron compounds. Bac- 



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