564 Prof. Woodhead, The results of 



able quantity of organic matter and a large number of micro- 

 organisms ; the results obtained must therefore be looked upon 

 as exceedingly satisfactory. 



Then came Dr Phelps' experiments followed by Dr Thresh's 

 paper in the Lancet*. The latter, beginning where Dr Houston 

 had left off, showed that one part of chlorine in a million of water 

 was fatal to the Bacillus coli in 24 minutes. He followed this up 

 with a series of experiments in which he found that 0'75 parts in 

 1,000,000 of water was still effective as a sterilising agent. Thresh 

 suggested, too, that any chlorine not taken up by the micro- 

 organisms or other organic matter present in the water should 

 be neutralised by the addition of bisulphite of soda. 



Repeatiijg these experiments but using Cambridge water 

 I found that all that was claimed for this method was under- 

 rather than over-stated, and that the limit at which chlorine 

 would act as a sterilising agent had not yet been reached, and 

 after carrying out a number of laboratory experiments I came to 

 the conclusion that here we had the key to the solution of the 

 question of the sterilisation of the Cambridge water. Continuing 

 I found that " bleach " solutions containing one part of chlorine in 

 two millions of water or even one part in four millions of water if 

 left to act for half an hour upon Bacillus coli added to the water 

 killed these bacteria. Typhoid bacilli added were similarly de- 

 stroyed. Again I found that on adding organic matter, such as 

 broth, to water containing these bacteria it was necessary, in order 

 to obtain complete sterilisation, to introduce a larger amount of 

 chlorine and that until much of this organic matter was saturated 

 with chlorine the chlorine did not attack the bacilli. As soon, 

 however, as a certain degree of saturation was effected the bacilli 

 were attacked and destroyed by any slight excess of chlorine. 

 These laboratory experiments were repeated time after time and 

 in each case with similar results. Continuing the experiments 

 suggested by Dr Thresh on the use of bisulphite of soda as a 

 " Chlorine killer " or neutraliser I found that where an excess of 

 chlorine was used in the presence of non-putrifying organic matter 

 the process of neutralisation both as regards taste and smell was 

 effective, but that in the presence of considerable quantities of 

 decomposing organic matter, although the chemical neutralisation 

 of the chlorine was effected, a peculiar iodoform taste and smell 

 remained and it was very difficult to get rid of either taste or 

 smell by continued storage or by the action of light, heat, etc. 

 Then it was found that Cambridge water to which chlorine 

 was added in the proportion of one part to six, seven or eight, 

 millions of water, though completely sterilised, retained not a trace 



* Lancet, London, 1908, Vol. ii. p. 1597. 



