158 TENTH ANNUAL REPORT OF THE 



pond 40x10 feet and containing water to the depth of one inch not less than 

 twenty pounds should be used. The sides should be kept constantly wet 

 with the liquid for an hour or more and the pond may stand over night with 

 the flow cut off. The water should then be turned on and no fish introduced 

 until the chloride of lime is thoroughly flushed away. This substance, even 

 in considerable dilution is fatal to fishes and may kill many in the stream 

 into which the ponds drain, and for a considerable distance below the point 

 at which their drainage enters. This may be obviated by reducing the rate 

 of the flushing process. 



Copper sulphate is extremely fatal to certain minute forms of vegetable 

 and animal life, especially the bacteria, and in some cases is effective in very 

 great dilutions. The least concentration 01 any disinfectant fatal to the 

 protoza of trout disease is unknown and, therefore, the quantities just 

 sufficient cannot be stated. Sufficient must be used to make a probable 

 excess, a solution in which no forms can reasonably be supposed to long 

 survive. Notwithstanding the high toxic power of copper sulphate for some 

 forms, it is not known that for the purpose under consideration it would be 

 any more effective than the chloride of lime, and its cost is about double that 

 of the latter. If for any reason it is more available it may be used in the 

 same proportion as the chloride of lime. It is highly toxic to brook trout. 

 Domesticated fry of a length of two to two and one-half inches are killed 

 within twenty-four hours by one part of copper sulphate in 6,000,000 parts of 

 water. Older trout are somewhat more resistant. The precautions when flush- 

 ing off the disinfectant are even mOre important than with chloride of lime. 



Of course a pond may be disinfected when full of standing water by 

 adding correspondingly larger amounts of the disinfectant. Wooden or 

 earth ponds may be treated in either of the ways described, but with less 

 likelihood of a thorough disinfection. The subsequent washing out should 

 be more prolonged than with a cement pond. 



At the beginning of this investigation a number of determinations of 

 the dissolved air in the station water supply was made. These were under- 

 taken partly because the apparatus for the purpose was available, and partly 

 for general data on fish cultural waters in this respect. No air defects were 

 indicated by the disease in progress. The results are of considerable interest 

 and are as follows: 



