April 21, 1905.1 



SCIENCE. 



615 



1 to 100,000, and is probably as high a 

 strength as need be used for killing newly 

 hatched larvae in .clear water. In the case 

 of half or two thirds grown larva? the imme- 

 diate death of the larvae was not secured, 

 but they were held in arrested development 

 for several days and slowly perished, some 

 few surviving two weeks, and this at 

 strengths between 1 to 100,000 and 1 to 

 500,000. The effect on full-grown and 

 nearly full-grown larva? is to hasten their 

 transformation to the pupal stage, such 

 larva? transforming within a few hours to 

 one day after the application of the copper 

 sulphate. Once in the pupal stage, no prac- 

 ticable strength of copper sulphate is ef- 

 fective against them. Strengths as great 

 as 1 to 1,000 were emj)loyed, and the pupsE 

 so treated were seemingly completely im- 

 mune from its effect, and ultimately trans- 

 formed to adult insects. The reason for 

 the almost absolute immunity of the pupal 

 stage is probably because in this stage no 

 food is taken, and the poison is purely 

 external and has no opportunity to act. 



It was further shown that copper foil 

 was very effective in destroying newly 

 hatched larvre. A piece of copper foil less 

 than six inches square killed, in two quarts 

 of water, the majority of young larvae with- 

 in 24 hours, and all within 48 hours. The 

 possibility of using copper foil, therefore, 

 to keep mosquito larvje out of small bodies 

 of comparatively pure water is shown. In 

 all of these tests check experiments, without 

 the addition of copper, were carried out. 



The general results shown are that newly 

 hatched mosquito larvfe are killed in com- 

 paratively pure water by practicable addi- 

 tions of copper sulphate, namely, between 

 1 to 100,000 and 1 to 5,000,000, the neces- 

 sary strength varying with the purity of 

 the water ; that copper foil exerts a remark- 

 able effect upon young larvae ; that the very 

 highest practicable strength, namely, 1 to 

 100,000, will check the development of half 



and two thirds grown larvte, and cause 

 their ultimate death ; that nearly full-grown 

 and full-grown larvae are induced to 

 promptly pupate, and that in the pupal 

 stage absolute immunity to copper salts is 

 shown. 



The practical application of copper sul- 

 phate seems, therefore, limited to the pro- 

 tection of small bodies of comparatively 

 pure water. It is further possible that in 

 the tropical countries, where much of the 

 drinking water is kept in cisterns, it will 

 have a distinct field for usefulness, and 

 possibly particularly against the yellow- 

 fever mosquito. Field tests in open ponds 

 failed to show any special value for copper 

 sulphate; it seemed to be precipitated too 

 quickly to have any important effect on the 

 larvae. The value of copper sulphate 

 against mosquitoes needs for its demon- 

 stration further tests, and particularly 

 under the tropical conditions referred to. 



Dr. H. W. Wiley, chief chemist, Bureau 

 of Chemistry, said : In regard to the use 

 of copper for purifying water, I have noth- 

 ing whatever to say except as it may per- 

 tain to water as a food. It is recognized 

 by all physiological chemists that water is 

 one of the principal foods and one of the 

 most necessary. The act of Congress au- 

 thorizing the investigation by the Bureau 

 of Chemistry of the adulteration of foods 

 includes beverages in the list of the articles 

 to be studied. The whole matter, therefore, 

 of the addition of copper to water which is 

 to be used for food purposes is intimately 

 related to other problems of a similar na- 

 ture which we have had under study in the 

 Bureau of Chemistry for the past twenty 

 years. There are two ways of considering 

 the evidence which has been accumulated 

 on this subject. One is to consider the 

 addition of certain substances, copper sul- 

 phate among them, to foods, as a process 

 involving the use of harmless substances; 

 the other view is to regard the substances 



