148 Proceedings of the Royal Society of Edinburgh. [Sess. 
found that a red-brown silver sol prepared by Bredig’s method was more 
powerfully bactericidal than an olive-green sol containing coarser particles 
prepared by the same method. Whether these amicrons produce surface 
effects or are taken up by the bacilli and converted into a soluble product 
within the organism is at present difficult to determine. But in view of 
the fact that colloidal sols of silver act more slowly than ionised silver, the 
latter view seems most probable. And it seems to me to receive some 
support from the experiments of Gompel and Henri,* who found, after 
intravenous injection of colloidal silver sols into animals, silver (spectro- 
scopically) in some of the secretions of the body. 
I am indebted to Miss A. W. Andrew, M.A., M.B., and to Miss 
Elizabeth Gilchrist, M.A., B.Sc., for help in the performance of some of 
the experiments. 
* Compt. Rend, de la Soc. de Biol., vol. lxi, p. 488 ( 1 906), 
(Issued separately October 20, 1919.) 
