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- 



FiG. 47. — Trichina. (After Hager-Mez.) 50 diameters. 



tiplication of microscopic plants and animals belonging 

 to the Algje 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-R after 

 method, in routine use by the State Board of Health and 

 the Metropolitan Water Board of Massachusetts, the 



