DETERMINATION oK A Til YSIOLOOICAL MKTIlnl). 15 



II' Miiv known inotliod of proveiitino- the j^rowth of mI^M' whs considered 

 trulv crteetive. it would under all cireunistanees be reconnuended. 



Because of the unsatisfactory results or the pn)hil)itive expense of 

 the present methods reconinieniled for riddinj^ reservoirs of alfja^, it 

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

 standpoint, one that would take into consideration the l)iolooical aspect 

 of the (juestion and perhaps furnish a solution, throu*>h a study of the 

 nhvsioloov of the orirtmisms under lal)oratorv conditions. A series of 

 investigations were therefore undertaken to discover, if possible, some 

 substance which, because of its extreme toxic etl'ect upon the algse 

 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 bv algte, two conditions had to be considered: The 

 remedy should not only be readily availalde and cheap enough for 

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

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

 man; the maxinunn amount necessary to kill the algte being far below 

 the amoiuit which could in an}' wa}' affect the consumer of the water. 

 Of the larg(^ numl^er of substances experimented with, few gave en- 

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

 I)hur dioxide in saturated aqueous solution at IG*-* C, diluted 1 to 1,000 

 and to 10, 000, will destroy man}' of the connnon forms of algie, 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 arc most of the acids. Locw '^ 

 tinds that magnesium sulphate is toxic in pure solution at 0.1: per cent, 

 and tliat oxalates are slightly more toxic; of the acids, 0.0001 percent 

 oxalic kills most of the cells of Spirogyra majiiscula in live days. 

 Migula '■ 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 



"Ci. Richter, Flora, 75: 4. 

 ^'Loew, Flora, 75: 368. 



''Migula, T^eber den Einfluss stark verduenter Sauren auf Algeiizellen, Breslau, 

 1888 (Original not consulted. ) 

 28480— No. 64-04 2 



