DETERMINATION OF A PHYSIOLOGICAL METHOD. 15 



If any known method of preventing the growth of algae was considered 

 truly effective, it would under all circumstances be recommended. 



Because of the unsatisfactory results or the prohibitive expense of 

 the present methods recommended for ridding reservoirs of algae, it 

 seemed advisable that the problem be taken up from an entirely new 

 standpoint, one that would take into consideration the biological aspect 

 of the question and perhaps furnish a solution, through a study of the 

 physiology of the organisms under laboratory conditions. A series of 

 investigations were therefore undertaken to discover, if possible, some 

 substance which, because of its extreme toxic effect upon the alga3 

 involved, would absolutely prevent their growth in water supplies. 



DETERMINATION OF A PHYSIOLOGICAL METHOD. 



In determining such a physiological method of dealing with reser- 

 voirs contaminated by algae r two conditions had to be considered: The 

 remedy should not only be readily available and cheap enough for 

 practical use in the largest reservoirs and by the poorest communities, 

 but under the conditions used it must also be absolutely harmless to 

 man ; the maximum amount necessary to kill the algae being far below 

 the amount which could in any way affect the consumer of the water. 

 Of the large number of substances experimented with, few gave en- 

 couraging results. Free chlorine at a dilution of 1 to 10,000, and sul- 

 phur dioxide in saturated aqueous solution at 16 C., diluted 1 to 1,000 

 and to 10,000, will destroy many of the common forms of algae, but sul- 

 phur dioxide and chlorine are likewise very injurious to animal life. 

 Silver has a very high toxicity, and were not the expense prohibitive, 

 would undoubtedly warrant extended tests. Mercury and lead are, 

 of course, out of the question, and zinc requires too high a concentra- 

 tion to be practically considered. The ordinary sodium, potassium, 

 and ammonium salts, are innocuous,* as are most of the acids. Loew 6 

 finds that magnesium sulphate is toxic in pure solution at 0.4 per cent, 

 and that oxalates are slightly more toxic; of the acids, 0.0001 per cent 

 oxalic kills most of the cells of Spirogyra majuscula in five days. 

 Migula c notes the effect of many of the organic acids, but the use of 

 these substances in the amounts requisite for treating a contaminated 

 water supply is entirely impracticable. 



EFFECT OF COPPER SULPHATE. 



Reviewing the experiments carried on in the Laboratory of Plant 

 Physiology, as well as the results obtained by other investigators, it 



Cf. Richter, Flora, 75: 4. 

 &Loew, Flora, 75: 368. 



c Migula, Ueber den Einfluss stark verduenter Sauren auf Algenzellen, Breslau, 

 1888. ( Original not consulted. ) 

 28480 No. 6404 2 



