Dr. George T. Moore, physiologist in charge of the laboratory of plant physiology, Bureau of Plant Industry, Washington, D. C., having heard of the troubles of a small town in Kentucky which were caused by algae in its reservoir, determined to remedy them. The town some years ago had built an expensive water system, and had suffered from these vegetable growths nearly all along. Dr. Moore found the water infested with anabama—7,000 filaments to the cubic centimetre—and smelling vilely. The reservoir was of about 25,000 gallons capacity, and, as the growths were so abundant, he determined on using a strong solution—1 to 4,000.00. About 200 pounds of blue vitriol were placed in a sack and hung from the stern of a boat, which was-rowed backwards and forwards, up and down and across the reservoir for several hours, covering the whole surface, so as to distribute the crystals of copper evenly. At first the evil smell grew worse, owing to the disturbance of the water having broken up many of the small sacs and set the oil free. At the end of twenty-four hours the greenish color began to disappear; at the end of forty-eight hours the green was entirely gone, and the surface was clear, but the water had a light-brown tinge due to the dead organisms held in suspension. At the end of the third day the w’ater was clear, sweet and completely cured of the disagreeable smell and taste. Tests showed that no algae were left. To make sure that the copper had not poisoned the water, Dr. Moore tested it a few hours after the dose was applied and found no trace of the copper remaining. It cost $12.50 to purify the reservoir, the only item of expense being the blue vitriol, which costs about six to seven cents a pound. The town, which had been spending thousands of dollars each year, ineffectually, has had no further trouble. After this successful experiment Dr. Moore attacked larger reservoirs, with equal success. In the fall of 1903 he sterilised a basin of 600,000,000 gallons in Massachusetts, formerly a part of the water supply system of Boston. At that time the water contained 10,000 organisms to the cubic centimetre. After the treatment he could not discover a single organism. This year only from thirty to sixty to the centimetre were found, and a very slight dose has killed these. Dr. Moore claims that the largest reservoirs in the world can be treated in the same way. When a very large surface has to be covered(he says) it is better to use several boats, or perhaps a small launch, in order that every part of the reservoir may be evenly treated. The treatment costs from fifty to sixty cents per 1,000,000 gallons. July is the best month to kill algæ. The organisms are then, so to speak, most relaxed, as they have not yet formed their spores and hardened themselves for the winter. All algae are not equally sensitive to the solution, so that the strength of the dose varies with the different species.