BACTERIA IN WATER 159 



in judging of the contamination of a water supply. The subject will be 

 more fully discussed in the chapter on Typhoid Fever. Here it may be 

 said that for work on water two attitudes are taken up in this country. 

 I ii>t. that of Houston, who recognises as typical qualities the following : 

 fluorescence in neutral red broth, production of acid and gas in lactose 

 peptone water, production of indol, production of acid and clot in litmus 

 milk (so-called " flaginac " reaction). Secondly, that of the English 

 Committee of 1904, which, on the one hand, laid stress on the additional 

 factor of non-liquefaction of gelatin, and on the other, attached less 

 importance to the production of indol and the occurrence of fluorescence 

 (see p. 355). 



With regard to saccharose fermentation, different strains of coli of 

 undoubted intestinal origin behave differently towards saccharose, but 

 when saccharose is fermented the occurrence is significant, as indicating 

 a great probability that the organism is intestinal in origin. 



(6) B. enteritidis sporogcncs and streptococci. As in the case of 

 sewage, the presence of these in a water may be sought for. The methods 

 are those which have already been given (p. 154). 



Much work has been devoted to the question of these faical streptococci 

 presenting specific characters by which they could be differentiated 

 from other streptococci. Houston has found that the prevailing type 

 of organism here is one which produces acid and clot in milk, reduces 

 neutral-red, and ferments saccharose, lactose, and salicin. It corresponds 

 to the streptococcus fcecalis of Andrewes and Horder. The important 

 point in this connection is to recognise that streptococci of such a type 

 exist in great numbers in human faeces, and that when in any circum- 

 stances faecal contamination is suspected, the isolation of streptococci 

 .strengthens the suspicion. 



With regard to the objects with which the bacteriological 

 examination of water may be undertaken, though these may 

 be of a purely scientific character, they usually aim at contribut- 

 ing to the settlement of questions relating to the potability of 

 waters, to their use in commerce, and to the efficiency of 

 processes undertaken for the purification of waters which have 

 undergone pollution. The last of these objects is often closely 

 associated with the first two, as the question so often arises 

 whether a purification process is so efficient as to make the 

 water again fit for use. 



Water derived from any natural source contains bacteria, 

 though, as in the case of some artesian wells and some springs,- 

 the numbers may be very small, e.g. 4 to 100 per c.c. In rain, 

 snow, and ice there are often great numbers, those in the first 

 two being derived from the air. Great attention has been paid 

 to the bacterial content of wells and rivers. With regard to 

 the former, precautions are necessary in arriving at a judgment. 

 If the water in a well has been standing for some time, 

 multiplication of bacteria may give a high value. To meet this 

 litlieulty the well ought, if practicable, to be pumped dry and 



