Two Groups of Flagellated Algae Serving as Indicators of Clean Water.

has long been recognized that there is a definite relationship between the sanitarj' condition of any given stream section and the organisms living in that section. This relationship is fairly well known for the larger free-swimming or attached animals. Such a relationship also applies to the microscopic creatures whether living on or attached to the bottom, or composing the assemblage of suspended forms known as rheoplankton. Whipple, Fair and Whipple (1) have summarized the findings of a number of workers and have classified the organisms as to degrees of pollution preferred by them. Such a classification of indicator organisms can be very useful to workers with water supplies, especially if it includes a sufficiently large variety of organisms so that some might reasonably be expected to occur in almost any sample taken at any time. Taking a sample which might contain animals as large as fish or shellfish may not be feasible, but where equipment includes a microscope or access to one, a small sample is easily taken and its microscopic life can either be concentrated by centrifuging, or killed by adding enough formalin to make a 3 per cent solution in which the organisms gradually settle and can be concentrated by decantation. In reservoirs and large streams or streams issuing from lakes, some microscopic forms are found at almost every season of the year. Flood conditions, or excessive turbidity may decrease plankton until no information will be available, but larger forms will likewise disappear under such conditions. If a small stream is under investiga-