. Preventive medicine and hygiene. rotein and also usually con-tains more moisture, which favors bacterial activity. The breaking down of the com]3lex protein molecules to smiplerand stabler compounds is usually spoken of as mineralization, and may GENERAL CONSIDERATIONS 775 be regarded as a series of oxidations. According to our present chemi-cal conception, it is really a series of hydrolyses. The complicatedmolecular structure of protein matter is analyzed into amino com-pounds of simpler and simpler composition, until nitrogen finally ap-pears in tlie form of ammonia. We know little of the
. Preventive medicine and hygiene. rotein and also usually con-tains more moisture, which favors bacterial activity. The breaking down of the com]3lex protein molecules to smiplerand stabler compounds is usually spoken of as mineralization, and may GENERAL CONSIDERATIONS 775 be regarded as a series of oxidations. According to our present chemi-cal conception, it is really a series of hydrolyses. The complicatedmolecular structure of protein matter is analyzed into amino com-pounds of simpler and simpler composition, until nitrogen finally ap-pears in tlie form of ammonia. We know little of the chemistry of theearly stages of protein decomposition. The process seems hopelesslycomplicated from the intricate structure of the molecule. Eventuallyfrom the seething caldron of molecular disintegration there appearsimpler substances, such as proteoses, peptone, ptomains, amins, leucin,and tyrosin, and other amino substances, as Avell as organic acids, indol,skatol, phenol, and finally sulphuretted hydrogen, mercaptan, carbonic. Fig. 98.—-The Nitrogen Cycle in Diagrammatic Vertical Section. acid, and ammonia. One of the final products of the process is carbondioxid, part of which passes into the atmosphere and part of which isretained in the soil as carbonates of alkalis or alkaline bases. Theammonia, as such, cannot be used by plants. Some of it may escapeinto the atmosphere, but for the most part it is retained in the soilas ammonium chlorid or ammonium carbonate. In the soil the am-monia is oxidized by the action of nitrifying bacteria into nitrates. Thisnitrifying action of bacteria, elucidated by Winogradski in 1888, wasone of the brilliant discoveries in bacteriology. Through his work andthat of later workers, it is now known that this process is usually accom-plished in two distinct steps. In the first stage the ammonia is oxidizedto nitrous acid. This is done by the nitrosobacteria. These nitrous ornitrite bacteria were called by Winogradski nitrosomonas and nitros
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