If 



STERILIZATION 175 



ubsequent recovery of the copper from the material, induced 

 Kroncke^ to adopt cuprous chloride ; others — e.g., the French 

 authorities in combating the cholera in 1892 — used the cheaper 

 cupric sulphate. Mr. Shrapnell Smith, of Liverpool, stated at 

 the Leeds Sanitary Congress, 1897, that he was using salts of 

 copper, and drawing air through the filter-beds by fans. More 

 recently sulphate of copper has been somewhat extensively 

 used in America and India for the removal of algae and the 

 bacterial contamination of rivers and reservoirs, but owing to 

 the expense this method is only of very limited application. 



In 1904 2 I confirmed the results obtained by Dr. Moore,^ 

 and found that copper chloride could be substituted for the 

 sulphate, and that the quantities required were so small as to 



use little apprehension as to injury to fish. 



The efficiency of different copper compounds depends on 

 the percentage of copper present in the salt ; for instance,* 

 I in 8,500 of copper sulphate, or i in 13,500 of copper chloride, 

 killed B. coli in three hours ; i in 7,000 of sulphate, or i in 

 10,000 of chloride, killed Staphylococcus pyogenes aureus in two 

 hours. 



Hence it appears that these salts might be useful in steri- 

 lizing oyster or watercress beds without danger. 



Even plates of metallic copper^ in ordinary water give off 

 enough of the metal in a so-called colloidal state to make the 

 liquid toxic to many algae and bacteria, and I am trying the 

 effect on sewage filtrates of passing them through copper gauze 

 to reduce the number of pathogenic organisms, with a view to 

 protecting watercress beds and oyster layings. 



Bassett Smith^ experimented with B. typhosus, coli, enteritidis, 

 B. dysenteric^ (Flexner), Micrococcus melitensis (the organism of 

 Mediterranean fever), and with ordinary water organisms, com- 

 paring the effect of copper with that of iron, zinc, lead, and tin. 

 His copper sulphate solutions were of i in 1,000, i in 10,000, and 

 I in 100,000 strength, and he observed that in all the dilutions 

 with distilled water B. typhosus was killed in under one hour ; 

 but in tap water the highest dilution required twenty-four hours ; 

 I in 10,000 required twelve hours. With B, coli in distilled or 

 tap water the highest dilution was insufficient to kill in twenty- 



^ Jonrn. f. Gasbeleuclit, xxxvi., 513. 



^ Journal of the Royal Sanitary Institute, vol. xxv. 



2 Bulletin^ Department of Agriculture, Washington, 1903. 



■* See also Green, Zcits.f. Hygiene, 1893, p. 495. 



^ P'or details I must refer to my paper, mentioned above, 



^ Journal of Preventive Medicine, July, 1904. 



