WATER 47 



work of Kolle and Gotschlich and others. This Report states, 

 4 ' It appears, therefore, that a rule might with advantage be 

 adopted to regard as choleraic every vibrio which is agglutinated 

 j n x IO oo at least by a serum the activity of which is I 4000 

 or over. For vibrios agglutinable by a cholera serum only in 

 stronger dilutions (i : 500 to I : 1000) the results should be con- 

 sidered as doubtful." 



Other tests which have been shown to be of value are the 

 haemolysis test and estimation of deviation of complement. 



A description of these tests would be out of place here, and 

 general and special text-books of bacteriology must be consulted. 



Significance and interpretation of results. 



The detection of the cholera spirillum or the typhoid bacillus 

 In a water, in whatever amount, is sufficient to condemn the 

 supply. The other results obtained in the bacteriological exam- 

 ination of water supplies are, however, only data from which an 

 opinion upon the purity or contamination of the water can be 

 deduced with more or less confidence according to the facts 

 available. 



Such deductions require much special experience and a 

 careful consideration of a number of facts, some of which will be 

 briefly discussed. 



As already explained, the contamination of water with excreta 

 or sewage is mainly dangerous (although not entirely so) from 

 the possibility that sooner or later it may be associated with con- 

 tamination with excrementitious matters containing the typhoid 

 bacillus and in this way an outbreak of enteric fever be set up. 

 Such specific pollution with the typhoid bacillus is almost invari- 

 ably associated with the addition of B. coli and streptococci to 

 the water, and while the typhoid bacillus is not readily detected 

 the existence of danger may be shown by these indicator organ- 

 isms. The vitality of B. typhosus in water and particularly the 

 relative vitality of this bacillus and B. coli in water is therefore of 

 great practical importance. On its negative side it is necessary to 

 know how far the absence or relative absence of bacilli of the 

 B. coli group can be accepted as presumptive proof that typhoid 



