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 thecircumstances and elements 
which unite to modify the condition ofa 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. 
