1909.] The Germicidal Action of Metals, etc. 85 



to a meeting of the Association of American Bacteriologists there has been 

 aio pubHcation, nor am I acquainted with their findings. The only observa- 

 tion known to me is that by Leedham-Green already noted, upon the negative 

 effects of unoxidised iron and the arrest of growth of bacteria when the iron 

 is allowed to undergo oxidation. The general conception has been that the 

 metal undergoes solution, and in this condition is directly active upon the 

 bacteria. 



As bearing upon the mode of action of metals, the results of the present 

 investigations may be briefly summed up. 



(i) Air drawn for one hour through water containing abundant colon 

 bacilli exercises no perceptible inhibitory action upon their subsequent 

 growth. 



(ii) Eelatively large amounts of pure zinc with large surface area placed in 

 water, contaminated with abundant colon bacilli, and allowed to act for one 

 hour, bring about a recognisable but not extreme destruction of the bacteria. 

 Aluminium and copper, under similar circumstances, have no perceptible 

 ■effect. 



(iii) When the same experiment is repeated, with the one difference that 

 the oxygen has been driven out of the water by previous boiling, none of 

 these metals has any decided influence upon the subsequent growth of the 

 bacteria. 



It is thus obvious that such bactericidal activity of zinc as manifests itself is 

 msociated with the coincident 'presence of oxygen. 



(iv) A much more intense bactericidal action is produced when air is 

 permitted to bubble for one hour through water holding the colon bacilli in 

 suspension, in the presence of aluminium, zinc and copper. Using a sufficiency 

 of the pure metal it is possible to render the water completely sterile with all 

 three metals, and that, when it contains abundant bacteria. 



(v) In the case of zinc and aluminium, the sterilisation process is accom- 

 panied by the production of easily recognisable amounts of peroxide of 

 hydrogen, and formation of hydrates of the two metals. 



(vi) While this is the case, the peroxide itself cannot be regarded as the 

 sterilising agent, and this because : — 



(ft) The amount of peroxide developed in one hour by bubbling air through 

 the like quantity of sterile water in the presence of zinc or aluminium, while 

 easily recognisable, is nevertheless very small in amount ; a similar dilution 

 of the peroxide added to a suspension of colon bacilli has no perceptible effect. 



(l>) Bactericidal action of the same or greater intensity is exerted by pure 

 copper under like conditions of experiment, and this with no associated 

 recognisable production of hydrogen peroxide. 



