Huff : RESPONSE OF MICRO-ORGANISMS TO COPPER SULPHATE 409 



fourteen hours within three days after treatment. In August, 1910, 

 when filter troubles were caused largely by Synedra and Mclosira 

 he found that a treatment of 1.67 parts per million increased the 

 filter runs from about two hours to a normal of thirteen hours 

 within three days after treatment. 



While in many places the organisms to be destroyed have been 

 determined before treatment, and the effects of the treatment upon 

 one or more abundant organisms noted in a general way, in a very 

 large number of cases where the treatment has been used, not 

 even a microscopic examination of the water has been made and 

 the species of algae present or causing the trouble were unknown. 

 Definite and detailed reports giving the conditions under which 

 treatments were made, the strength of the treatment, followed 

 up by the results of the treatment upon various organisms, as can 

 be determined only by regular and frequent microscopic counts of 

 organisms present in the treated water, have in most cases been 

 sadly neglected. The following paper shows the effect of copper 

 sulphate upon several organisms common in Vadnais Lake. 



The method used for determining the number of organisms is 

 known as the Sedgwick-Rafter method, and may be described 

 briefly as follows. 



A sample consisting of 500 cubic centimeters of water is placed 

 in a cylindrical funnel and filtered through a layer of fine sand 

 about two centimeters in thickness. This sand strains out practi- 

 cally all organisms. When only 5 cubic centimeters of water re- 

 main unfiltered, the process is stopped, the sand and water are 

 emptied out into a small beaker, and the sand thoroughly rinsed 

 with this water, which is then carefully drained off into a clean 

 beaker. The sand is rinsed again, this time with five cubic centi- 

 meters of distilled water, which removes practically all remaining 

 organisms from the sand. The water used for this second rinsing 

 is now mixed with that used for the first, and this is decanted two 

 or three times to free it from all sand particles. This ten cubic 

 centimeters is thoroughly mixed with a pipette, and while the or- 

 ganisms are still uniformly distributed throughout the mixture, a 

 single cubic centimeter is removed and placed in the Sedgwick- 

 Rafter counting cell, for microscopic examination. The Sedgwick- 

 Rafter cell is exactly one millimeter in depth, and by proper ad- 



