238 ESSENTIALS OF BOTANY 
The occurrence of blue-green and green alge in city 
water-supplies is often a matter of serious importance, as 
it may give rise to very disagreeable tastes and smells. 
Some of the odors have been described as the moldy, the 
fishy, the «‘ pig-pen” odor, and soon. Various means have 
been adopted for getting rid of the organisms, and most 
of them (including some animalcules) may readily be de- 
stroyed by adding a small proportion of copper sulphate 
to the water in the reservoir.1 A bag of the copper salt 
trailed behind a boat rowed about over the surface will 
readily supply the needed amount of sulphate. Some of 
the most objectionable organisms are killed by as small a 
proportion of copper sulphate as one pound to five or ten 
million pounds of water, and in such a dilute solution as 
this the salt is not capable of exerting any poisonous 
action upon the drinkers of the water. 
1See Bergen and Davis’ Principles of Botany, pp. 170, 171. See also 
Whipple’s Microscopy of Drinking Water, Chapter IX, John Wiley & Sons, 
New York. 
