122 ELEMENTS OF APPLIED MICROSCOPY. 
of importance in the detection of admixture of its water 
with that from some other source. The great importance 
of the: microscopical examination of drinking-water lies, 
however, in its application to the study of those organisms 
which produce tastes and odors in reservoirs. Such 
tastes and odors are in almost all cases due to the mul- 
Fic. 47.—Tricuina. (After Hager-Mez.) 50 diameters. 
tiplication of microscopic plants and animals belonging 
to the Alge and the Protozoa; and the study and control 
of these organisms depends upon the systematic use of 
the microscope. 
A considerable concentration of the sample must, of 
course, precede the microscopical examination of drink- 
ing-water; and this is usually accomplished by filtration 
through a layer of fine sand. The Sedgwick-Rafter 
method, in routine use by the State Board of Health and 
the Metropolitan Water Board of Massachusetts, the 
