Huff: RESPONSE OF MICRO-ORGANISMS TO COPPER SULPHATE 417 



dard units were due to Syncdra pnlchclla. The remaining 4,700 

 units were made up of other diatoms, green algae, blue-green algae, 

 and protozoa, the numbers of which are brought out in other figures. 

 The treatment consisted of about one part of copper sulphate to 

 12.000.000 parts of water. It was responded to by most of the 

 forms, but was not nearly so effective as the slightly heavier treat- 

 ments given later. Within less than two weeks the total number of 

 organisms had dropped to 2,400, with about 1,100 standard units 

 of Synedra. Early in July, Synedra began to show a rather rapid 

 increase in numbers, and by July 12, had reached 8,260 standard 

 units per cubic centimeter, bringing the total number of organisms 

 per cubic centimeter up to approximately 9,700 standard units. A 

 second treatment of one part of copper sulphate to 10,000,000 parts 

 of water brought very decided and satisfactory results. Within ten 

 days after the treatment the total number of organisms dropped 

 from 9,700 to less than 100 per cubic centimeter, where they re- 

 mained for more than four weeks. 



The rate of increase or multiplication in some of the diatoms is 

 mteresting, and a glance at the chart (figure 1) will show how very 

 rapidly they increase when once conditions become favorable for 

 their growth. The following figures for Synedra pulchella show 

 how it increased in eight days under normal conditions in Vadnais 

 Lake : 



Date Individuals per 



cubic centimeter 



24 225 



25 520 



26 1080 



27 3020 



Judging from these figures, Synedra may, under favorable con- 

 ditions, double its number in about twenty-four hours, and at this 

 rate of increase a comparatively small number surviving after the 

 treatment, or entering the lake through the inlet after the treatment, 

 will be sufficient to replenish the lake in a very short time. 



On August 27. with the total number of organisms about 4,000 

 standard units per cubic centimeter, a third treatment of copper sul- 

 phate of the same strength as the second (1 to 10,000.000) was 

 given the entire lake. The reduction of organisms that followed 

 was similar to that of the second treatment, but required about 

 eighteen days to bring the number below 100 standard units per 

 cubic centimeter. Synedra and some of the other forms responded 



