Kirchner — Bacteriological Examination of River Water. 267 



of utilizing the nitrogen, and, in conjunction with other 

 elements, of elaborating it into plant tissues which may serve 

 as food for animals and for man. The bacteria, acting upon 

 dead organic matter and upon the waste products of meta- 

 bolism, convert the nitrogen compounds into a form which 

 again becomes available for the growth of plant and animal 

 life. It must be evident that the part which bacteria play in 

 this cycle of changes is not only important but essential for 

 life activity, and in the problem of sewage purification these 

 phenomena must receive proper consideration. 



A river-basin, representing the lowest level for the region 

 through which it flows, is the natural receptacle for all waste 

 products. The variety of the material which finds its way 

 into a river is very great, and the circumstances and elements 

 which unite to modify the condition of a river are so numer- 

 ous, that it should not be surprising that often great difficult- 

 ies are encountered, not only in obtaining definite results, but 

 also in arriving at their proper interpretation. In order, there- 

 fore, to fully understand the subject of pollution of streams 

 by sewage, it would be necessary to have at least a thorough 

 knowledge of the scope and methods of a bacteriological 

 examination. 



Before any bacteriological work can be satisfactorily under- 

 taken, it is essential that the laboratory equipment be adequate 

 and that the assistants be competent and capable of attending 

 to their respective duties. It is necessary that all persons 

 connected either with the collecting, handling or examination 

 of samples, and that all persons working in the laboratory be 

 imbued with what might be called the " bacteriological idea." 

 By this expression is meant a thorough knowledge and appre- 

 ciation of the fundamental principles of bacteriology ; for no 

 trustworthy work can be done, unless all persons engaged in 

 the undertaking understand the objects and methods of steril- 

 ization and appreciate the sources and means by which a 

 sample of water or any portion of the work may be contami- 

 nated. Reliable results are obtainable only with unity of 

 purpose, uniformity of methods, and interdependence of those 

 engaged in the undertaking. 



