200 Journal of Agricultural Research vol. xx, No. 3 



5. In the 1 to 100,000 dilution, which was tried merely to ascertain 

 whether this concentration would kill quickly, the snails became prostrate 

 immediately upon being immersed and remained motionless, but they 

 almost all revived after immersion for one hour. 



• The actual physiological effect of the copper salts on the snails has not 

 been determined. Within a few minutes the snails immersed in a dilute 

 copper-sulphate solution lie prostrate, being apparently unable to cling 

 to the sides of the jar. A mucous albuminoid substance is exuded, and 

 frequently feces, eggs, and even the penis, are extruded. It is highly 

 probable that the poisoning effect is due at least in part to inactivation 

 of enzyms necessary to life. Peters and Burres (15) showed that the 

 concentrations of copper sulphate necessary to kill Paramoecium and 

 Stentor were approximately the same as those necessary to inactivate 

 their normal enzyms. It was thought that possibly there was a special 

 tendency in snails to absorb copper, since this metal is an important con- 

 stituent of the blood and is found only in minute traces in the normal 

 environment. However, analyses of snails killed in copper-sulphate 

 solutions, compared with normal snails, failed to show appreciably 

 greater quantities of copper. Furthermore it was found that the snails 

 succumbed as quickly in a few cubic centimeters of the solutions as they 

 did in large quantities. Five specimens of Limnaea bulimoides were 

 killed in 10 cc. of a 1 to 1,000,000 solution, yet the total amount of 

 copper present was only about 0.0025 m g m > or 0.005 rngm. per snail. 

 By analogy with Helix pomatia, which was shown by Dubois (8) to con- 

 tain 6. 1 1 mgm. of copper per 100 gr. of body weight, a specimen of 

 Limnaea should normally contain several milligrams of copper. If 

 the mode of action of the copper salts is by inactivation of enzyms, the 

 similarity in effect of such varying dilutions as 1 to 500,000 and 1 to 

 2,000,000 is more readily explained. 



The effect of a 1 to 1,000,000 copper-sulphate solution was also tried 

 on the eggs of Physa nuttalli and of Limnaea bulimoides. Eggs in intact 

 gelatinous masses were apparently uninjured by the copper solutions in 

 14 days, though the inclosed embryos seemed to grow more slowly than 

 the controls. 



There are a number of factors which influence the effect of copper 

 sulphate on organisms in water, the most important being temperature, 

 presence of algae, alkalinity, and organic matter in solution. As regards 

 temperature, no extended experiments were carried out, but experiments 

 with a 1 to 1,000,000 solution were carried out at temperatures of from 

 1 5 to 27 C, and the snails apparently succumbed as quickly at the 

 lower as at the higher temperature. Water in which snails were to be 

 destroyed would probably not fall below 15 C. in temperature. Alkalin- 

 ity of water, to the extent normally found in natural ground waters, 

 appears to have little effect on the action of the copper salts, although 

 copper sulphate is precipitated as basic sulphates or carbonates in 



