CONTENTS 



CHAPTER XII. 



INFLUENCE OF ARSENIC ON BACTERIAL ACTIVITY 



Occurrence of Arsenic 118 



Factors Influencing Solubility 118 



Ammonifiers 119 



Nitrification 119 



Nitrogen Fixation 120 



How Does the Arsenic Act? 120 



References . 126 



CHAPTER XIII. 



EFFECT OF HEAT AND VOLATILE ANTISEPTICS ON SOIL BACTERIA 



Influence on Plant 127 



Effect on Properties of Soil 128 



Hypotheses to Account for Observed Phenomena 133 



Koch's "Direct Stimulation" Theory 133 



Hiltner and Stormer's Indirect Theory 133 



Russell and Hutchinson's Protozoan Theory 135 



Greig-Smith's Bacteriotoxin Theory 138 



References . ...... 138 



CHAPTER XIV. 



INFLUENCE OF SALTS ON THE BACTERIAL ACTIVITIES OF THE SOIL 



Calcium Carbonate 139 



Lime 141 



Gypsum 142 



Calcium Chloride 142 



Iron Sulphate . . . . , . 



Magnesium Salts 



Manganese 



Potassium Salts 144 



Sodium Salts 145 



Variation in Effect Produced .146 



Stimulating Action 147 



Toxicity of Various Salts .149 



Reference 149 



HAPTER XV.C 



INFLUENCE OF MANURE ON THE BACTERIAL ACTIVITIES OF THE SOIL 



Number 151 



Ammonification and Nitrification 



Loss of Nitrates - 153 



Green Manures 



Reference 159 



CHAPTER XVI. 



THE SOIL FLORA 



Koch Gelatin-Plate Method 160 



Hiltner and Stonner Dilution Method . . . . 160 



Defects of Plate Method 160 



Value of Bacterial Counts 161 



