614 



SCIENCE. 



[X. S. Vol. XXI. Xo. 538. 



Avhich we used would be too weak to have 

 much, if any, effect in reducing bacteria. 



So much for the results shown by the 

 analyses. The practical value of the treat- 

 ment was observed in the very great dim- 

 inution in the number of complaints of 

 bad water, which had been unusually large 

 just previous to the experiment. 



The cost of the experiment was between 

 $60 and $70, which was for the copper sul- 

 phate used, or less than ten cents per mil- 

 lion gallons treated. 



Dr. C. L. Marlatt, entomologist, Bureau 

 of Entomology, said: In the original pub- 

 lication on the use of copper sulphate 

 against algae, a paragraph was given indi- 

 cating the results of certain incidental ex- 

 periments with mosquito larvse. These 

 experiments indicated that a strength of 

 1 to 40,000 was apparently necessary to 

 kill presumably nearly full-grown larvae. 

 The strength indicated is greater than is 

 practicable for water to be used for do- 

 mestic purposes, but a distinct toxicity of 

 the copper sulphate for mosquito larvae was 

 shown. A series of experiments was imme- 

 diately instituted in the laboratory of the 

 bureau to determine the exact value of cop- 

 per sulphate in this field. The common 

 method of destroying mosquito larvae in 

 comparatively still bodies of water is in 

 the use of kerosene oil. This, however, has 

 the objection of rendering the water \m- 

 palatable, and the copper salt seemed to 

 offer a possibility of the use of a substance 

 which would not injure water for domestic 

 consumption. 



During the spring and summer of 1904 

 more than 75 experiments were made with 

 copper sulphate, beginning with the first 

 larva^ available in the spring, and continu- 

 ing until autumn. Tests were made with 

 various kinds of water, namely, distilled 

 water, hydrant water, foul water from old 

 rain-water barrels of long standing, and 

 water from outdoor ponds more or less 



soiled with earthy matter and animal and 

 vegetable life. The mosquito larvai sub- 

 jected to the different tests were various 

 species of Culex and Anopheles ; the former 

 the common biting mosquito, and the latter 

 representing the species responsible for the 

 conveyance of malaria. 



The importance of the water conditions 

 was at once evident. The copper sulphate 

 showed very considerable effectiveness in 

 comparatively pure water, and lost its ac- 

 tion very quickly in foul water or water 

 containing much earthy matter, in the lat- 

 ter cases the copper being quickly precipi- 

 tated with the foreign matter in the water. 

 The use of distilled water and compara- 

 tively pure hydrant water was of value in 

 determining the direct toxicity of copper 

 sulphate ; in other words, in such water the 

 killing of the larva? could not be charged to 

 the destruction of the food in the water, 

 which might reasonably be offered as the 

 explanation in the case of more or less foul 

 water in which mosquitoes ordinarily breed, 

 containing quantities of vegetable and ani- 

 mal life. Mosquito larvae were killed in 

 distilled and pure hydrant water quickly, 

 and in the check jars in which no poison 

 was placed they remained in healthy con- 

 dition indefinitely, or at least exceeding a 

 week or ten days. 



The larval conditions also exerted a very 

 marked influence on the results. The 

 young larviB are killed with minute addi- 

 tions of copper sulphate. The strength 

 necessary to effect the prompt death of the 

 larvsE increases very quickly with the age 

 of the larvae. In comparatively pure water, 

 such as hydrant water, a strength of from 

 1 to 100,000 to 1 to 5,000,000 killed newly 

 hatched larvae with promptness, that is, 

 within 24 to 48 hours. Any strength of cop- 

 per sulphate between 1 to 100,000 and up- 

 wards is stated to be a practicable strength 

 for use in water for domestic purposes. 

 One to 500,000 was almost as effective as 



