6 GENERAL CONSIDERATIONS 



this way he has differentiated the strains isolated from different 

 sources into a large number of different varieties. His lines of 

 classification have been followed by other workers. The value 

 of their employment must depend upon the light they shed upon 

 the differential origin of the different strains. For example, to 

 demonstrate that the fermentation of saccharose test is of value 

 it has to be shown that organisms which ferment this sugar 

 have a greater or a lesser significance than those which do not 

 ferment saccharose. If all B. coli in excreta, or even a pre- 

 ponderance of them, fermented saccharose, then the presence of 

 a B. coli in water or food which was without this property w r ould 

 have but little significance as an indicator of excreta. Nothing 

 of the sort, however, has as yet been established, and the same 

 may be said for the other sugar-alcohol tests, and interesting 

 as these tests are and valuable for research work, it cannot be 

 said that their employment for routine work adds information 

 of material value. 



The testing of the pathogenicity of isolated strains of B. coli 

 has not proved of any practical utility for public health work. 



For routine practical work it is important to have some 

 definite and easily carried out system for recording B. colt 

 organisms and noting how far they conform to the type most 

 frequently met with in sewage. In 1905 the writer suggested 1 

 that the expression excretal B. coli should be used for organisms 

 giving all the following characters : 



A short rounded bacillus. 



Translucent non-corrugated growth on gelatin slope. 



Non-liquefaction of gelatin (two weeks). 



Acid production in litmus milk with coagulation (within two- 

 weeks). 



Fermentation of lactose with production of acid and gas. 

 glucose 



Neutral red reaction (in glucose media). 



Production of indol in peptone water. 



Since practically all organisms which ferment lactose also 

 ferment glucose the fermentation of glucose may be omitted > 



1 Lancet, Feb. 4, 1905. 



