. Agricultural bacteriology. Bacteriology, Agricultural. METABOLISM 223 • stock but from the straw, particles of earth, etc., that stick to the manure. These bacteria increase in number until at the end of four weeks there may be 1000 per gram of substance associated with these. Hence, we may conclude that the absence of nitri- fication which has been noted by various workers when organic matter'is present may be due to some of the following factors: (1) Excessive quantities of soluble organic matter. This has been repeatedly found to be the case where excessive quantities of carbohydrates hav
. Agricultural bacteriology. Bacteriology, Agricultural. METABOLISM 223 • stock but from the straw, particles of earth, etc., that stick to the manure. These bacteria increase in number until at the end of four weeks there may be 1000 per gram of substance associated with these. Hence, we may conclude that the absence of nitri- fication which has been noted by various workers when organic matter'is present may be due to some of the following factors: (1) Excessive quantities of soluble organic matter. This has been repeatedly found to be the case where excessive quantities of carbohydrates have been added to the media. (2) A low per- centage of potassium as suggested by Renault. (3) The physical and chemical properties of the medium, as noted by Stevens and Withers. (4) The presence of organic acid, as is the case in peats and forest soils. In this condition it is the acid reaction which interferes with the process and not the organic matter present. (5) A substance may be toxic when tested by the solution method, whereas in the soil it may be inert or actually beneficial. Energy.—The nitrifying organisms are devoid of chlorophyll and function best in the dark, yet they synthesize from the carbon dioxid complex organic compounds. The energy necessary for this synthesis is obtained by the nitrosomonas from the oxidation of ammonia: 2NH3 + 3O2 = 2HNO2 + 2H2O + and by the nitrobacter from the oxidation of nitrous acid: 2HN02 + O2 = 2HN03 + Lafar points out that if the quantity of nitrogen oxidized per unit of time be taken as the standard for measuring the chemical energy of these organisms, the nitrosomonas will be found the most active of the two. From this fact he concludes that the conversion of the trivalent nitrogen of nitrous acid into pentav- alent nitric nitrogen requires the expenditure of a greater amount of internal force than is needed for the first step in the oxidation. Metabolism.—The metabolism of these organisms has, therefore
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