198 Journal of Agricultural Research vol. xx. N0.3 



harmless in the dilutions which are lethal to the single-celled organisms. 

 Copper is, in fact, a normal constituent of their tissues and replaces iron 

 in the blood of some invertebrates. Experiments by the writer, as well 

 as by others, show that copper, 1 part per million, is not injurious, at 

 least within 48 hours, to annelids, crustaceans, or aquatic insect larvae. 

 Of vertebrate animals, fish are highly susceptible, various species being 

 affected by 1 part of copper sulphate in from 500,000 to 10,000,000 

 parts of water. Amphibians are immune to dilutions of 1 to 1 ,000,000. 

 Contrary to popular opinion, copper is not highly toxic to mammals and 

 can, in fact, be taken by the mouth in considerable quantities without 

 injury. Five to 10 gr. (0.32 to 0.64 gm.) can be taken as an emetic. 

 Horses and cattle can take 3.9 to 7.7 gm. and sheep 1.3 to 2.6 gm. It 

 is evident, therefore, that copper salts in high dilution have a selective 

 effect on various organisms, being particularly destructive to single- 

 celled organisms, certain molluscs, and fishes. For destroying aquatic 

 snails, therefore, copper sulphate can be used in perfect safety so far 

 as any possibility of injury to man or domestic animals from drinking 

 or bathing is concerned, without injuring the water for irrigation pur- 

 poses, and without destroying other higher organisms, except certain 

 species of fish. 



After it was found that very dilute solutions of copper salts are specifi- 

 cally toxic to Limnaea (Galba) bulimoides, experiments were carried out to 

 determine their effect on other species of snails and also to ascertain as 

 accurately as possible the effect of varying concentrations of the salts. 

 In all of these experiments only chemically pure copper sulphate was used. 

 Preliminary experiments showed that there was no appreciable difference 

 in effect whether distilled water or the local tap water was used in the 

 experiments ; therefore the tap water was used except for making up the 

 stock 0.1 per cent and 0.01 per cent solutions. All the local species of 

 snails of which sufficient numbers could be obtained were tried. It was 

 not practicable to experiment with the species of snails which have actually 

 been incriminated as. the intermediate hosts of important flukes of man 

 and domestic animals, but a greater variety of snails than those which 

 have been incriminated were used, including representatives or close 

 allies of all the incriminated families and in some cases genera. 



Of the species used, Planorbis callioglypius belongs to the family Plan- 

 orbidae, to which belong Bullinus, Planorbis, and Physopsis, intermediate 

 hosts of Schistosoma haematobium and 5. mansoni; Goniobasis, according 

 to Pilsbry, is closely akin to Melania, intermediate host of Paragonimus, 

 Metagonimus, and Clonorchis; Fluminieola belongs to the family Amni- 

 colidae in common with Blanfordia, intermediate host of Schistosoma 

 japonicum; several species of Iyimnaea serve as intermediate hosts for 

 Fasciola hepatica. 



Some difficulty was encountered in correctly reading the effect pro- 

 duced on the snails, and all earlier experiments had to be discarded. 



