EFFECT OF ORGANIC SUBSTANCES ON COPPER SULPHATE 291 



the reduction in 5 minutes was 67 per cent in a concentration of 0.38 

 parts of copper per million, but all the organisms had not been killed 

 in 24 hours. Such results indicate an extreme range of resistance 

 to copper among these organisms. The 42 organisms which sur- 

 vived the treatment for 24 hours lived 288 times as long as the 250,- 

 ooo which died in less than 5 minutes. 



Effect of concentration. This great variability is also shown in a 

 study of the effect of various concentrations. 



The average percentage survival after 24 hours in all experi- 

 ments with 0.38 parts of copper per million was 0.19; with 0.76 

 parts, 0.07; with 1.26 parts, 0.04. Notwithstanding the fact that 

 99.8 per cent are killed by a concentration of 0.38 parts, there 

 are still 0.04 per cent which can withstand the action of a copper 

 solution four times as concentrated. 



This tremendous variability is of vital importance, not only in 

 questions of sterilization of water by heat, freezing, or chemicals, in 

 all of which cases such a variability has been shown to exist, but 

 in the far more important questions of the self-purification of streams 

 and the longevity of the typhoid bacillus in the water. Most cases 

 of typhoid fever, contracted from drinking-water, have undoubtedly 

 come from these few resistant forms rather than from those which 

 are known to have perished in the natural stream. A removal 

 of 99.99 per cent of the typhoid organisms may sound like security 

 but actually means high typhoid rates. The importance of this 

 residual hundredth of a per cent cannot be overestimated, owing to 

 the very fact that it is so resistant. 



REFERENCES. 



BASSETT-SMITH, P. W. Jour. Prev. Med., 1905, 13, p. 388. 



ELLMS, J. W. Jour. N. E. W. W. A., 1905, 19, p. 496. 



JOHNSON, C. A., AND COPELAND, W. K. Jour. Infect. Dis., 1905, Suppl. No. i, p. 327. 



KRAEMER, H. Proc. Amer. Phil. Soc., 1905, 49, p. 51. 



STILES, P. G., AND BEERS, W. H., JR. Am. Jour, of PhysioL, 1905, 14, p. 133. 



TRUE AND OGLEVEE. Bot. Gaz. 1905, 39, p. i. 



SULLIVAN, E. C. Jour. Am. Chem. Soc., 1905, 27, p. 976. 



