199 



leads in u few liours to the deatli of the tadpoles. This 

 observation has been confirmed by Ringer,t and more 

 recently by Eoaf and Whitley, J who have also shown that 

 a trace of colloidal silver in suspension leads rapidly to a 

 fatal resnlt, while colloidal platinnni under like conditions 

 is (jnitc harmless. 



It has been suggested to me by Professor B. Moore 

 that possibly tho cause of the poisonous action in some 

 organisms and immunitv in others, mav be due to those 

 organisms which are poisoned throwing out excretory 

 substances Avhich dissolve copper and form soluble 

 poisonous compounds which are absor1)ed, and so lead to 

 the toxic eifects. 



'^riie matter lias also been discussed recently as one 

 which may be of importance in killing algae and 

 pathogenic organisms in water supplies. Dr. G. Moore, 

 of Washington, found that one part in fifty millions was 

 sufficient to kill oft' fresh-water algse in water-cress beds, 

 and that 1 in 100,000 would kill cholera and typhoid 

 oi-ganisms in 4 to 5 hours, llideal and Baines (1904) 

 found that 24 hours in a copper vessel was sufficient to 

 free the water from typhoid and colon bacilli. Bassett- 

 Smith, ' as the result of a number of experiments, states 

 that " Bacillus ti/phosus is more easily killed than others 

 of the coli grou]), l)eing destroyed in 12 hours with tln^ 

 1 in 10,000 dilution "" [sulphate of copper]. He also timls 

 that " Zinc, or iron coated with zinc, though less rapid in 

 its action than copper, yet after 24 to 48 hours appears to 

 free the water from typhoid organisms, and is the most 



I ]l)id., 1SU7, vol. i4-2, p. .xiv. (Ph,\>ioi. Soc. I^roc.) 

 l Coramnnicated by ihu authors (Biuclifinieal Dopartmoit, Uuivei^ity 

 of Liverpool) — the paper not bciiiK vet published. 



■'• Juurn. of Prcvoitivc Medicine, July, I'JOo. 



