The President's Address. By G. S. Woodhead. 



215 



non-spore-bearing organisms were killed off by one part per 

 million of available chlorine.* 



Fig. 



22. — Summary of Chlorine Sterilization Experiments (1 in 1,000,000) with 

 water experimentally contaminated with B. coli communis and dead organic 

 matter, i.e. neutral broth. 



Determined to push the matter further, and continuing my 

 experiments, I found that one part of available chlorine in seven 

 million parts of water was sufficient to destroy the small number 

 of non-spore-bearing organisms present in pure chalk water, and 

 I was able to demonstrate both by plate cultivations and by 

 the incubation of large quantities of water, to which McConkey's 

 concentrated bile salts medium was added, that this minute 

 quantity, acting for a period of twenty minutes, was sufficient to 

 eliminate the B. c. c. from clear chalk water in which carbon 

 dioxide in an easily separable form was held. In some earlier 

 experiments I had demonstrated that the cholera vibrio and 

 the typhoid bacillus reacted not only to hypochlorous acid but 

 to other antiseptics much as does the B. c. c. I felt justified, 

 therefore, in later investigations in concentrating my atten- 

 tion on the B. c. c. Having determined how easy a matter it 

 is to kill this .micro-organism by weak solutions of chloride of 

 lime, solutions that gave merely a violet end-point, or very faint 

 blue, reaction with starch and iodide of potassium, I found 

 that water so treated and reacting was absolutely tasteless, 

 though impartial observers whom I could persuade to partake of 

 both treated and untreated samples agreed — when they did not 



* The available or reacting chlorine is utilized as indicating the amount of 

 hypocblorous acid present, and therefore the oxidising power of the solutio l. 



