. Preventive medicine and hygiene. s of events constitutingthe nitrogen cycle largely depends upon the plant kingdom. The im-portant phases of the cycle occur upon the soil and in its superficiallayer. It will presently bo seen that this cycle has a fundamental im-portance in sanitary science, and lias a special significance in prevent-ing soil pollution, in the purifieation of water, and in the disposal of 774 GBNEEAL CONSIUEEATIONS sewage. It is evident that any permanent break in this cycle wouldresult in the cessation of life upon the earth. As soon as an animal or plant dies its protein c
. Preventive medicine and hygiene. s of events constitutingthe nitrogen cycle largely depends upon the plant kingdom. The im-portant phases of the cycle occur upon the soil and in its superficiallayer. It will presently bo seen that this cycle has a fundamental im-portance in sanitary science, and lias a special significance in prevent-ing soil pollution, in the purifieation of water, and in the disposal of 774 GBNEEAL CONSIUEEATIONS sewage. It is evident that any permanent break in this cycle wouldresult in the cessation of life upon the earth. As soon as an animal or plant dies its protein constituents are atonce attacked by putrefactive bacteria. The proteolytic microorganisms(aided by the larvae-of insects) growing in and upon the nitrogenousmatter break it up into secondary and simpler products, which havea striking resemblance to the cleavage products of gastric and pancreaticdigestion. Some of the putrefactive bacteria, of which the Bacillussubtilis and the Bacillus proteus are important types, liquefy protein I. iKInetic Energy]Fig. 95.—The Nitrogen Cycle. matter during the process of putrefaction. Other bacteria, of which thecolon bacillus is a type, break down organic matter without evidentliquefaction. Very many other species of bacteria take part in thisstage of the cycle. For the most part the microorganisms pathogenicfor man are killed during the process of putrefaction; they die in thestruggle for existence. The processes of decomposition are essentiall}-the same, whether the organic matter is the carcass of an elephant, abeetle, a tree, or a leaf, provided that the necessary moisture, warmth,and other conditions for bacterial growth are present. The breakingdown of vegetable matter is slower and more difficult than the break-down of animal matter. This is due in part to the fact that the lattercontains larger percentages of putrescible protein and also usually con-tains more moisture, which favors bacterial activity. The breaking down of the com]3l
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Keywords: ., bookauthorwh, bookcentury1900, bookdecade1910, booksubjecthygiene
