BACILLUS COLI 51 



to one hundred times less than that detectable by chemistry.* It is, 

 however, important to bear in mind that something more than the 

 mere presence of B. coli must be ascertained. The comparative 

 numbers present, the relative abundance, and the general character 

 and source of the water must be considered. Waters containing no 

 B. coli in 100 c;c. are of course of a high degree of purity.f In 

 upland surface waters the presence of B. coli in such a small amount 

 as 1 c.c, may be sufficient to condemn the waters. Certainly drinking- 

 water from a deep well should contain no B. coli. The presence in 

 a water of B. coli in conjunction with streptococci or even the spores 

 of B. 67iteritidis sporogenes, or both, would of course indicate serious 

 pollution. 



The differential diagnosis of B. coli from its allies or other 

 organisms is not always a simple matter. An adherence to the 

 characteristics set out above will generally prove safe guidance, but 

 rehance should not be placed upon any single character or test. 

 The tendency to adopt some rapid and easily-applied test for this 

 organism is strongly to be deprecated, as likely to lead to error. 

 Nothing can take the place of the careful study and sub-culture of 

 the suspected organism in this and in all other species. At the same 

 time, it has been found that diagnostic aid is obtained by a 

 comparison of some of the biological characters of the colon and 

 allied groups of bacteria. They may be divided into four divisions : — 

 (1) The proteus group, the members of which are motile, liquefy 

 gelatine, produce gas in glucose and sucrose but not in lactose, curdle 

 and acidulate milk very slowly, and usually produce indol ; (2) the coli 

 group include motile bacilli, producing gas in glucose and lactose, 

 curdle milk rapidly, nearly always produce indol, but do not liquefy 

 gelatine, and do not retain Gram's stain; (3) the group including 

 B. lactis cerogenes are non-motile bacilli, which do not liquefy gelatine 

 but which curdle and acidulate milk and ferment sugars other than 

 glucose; and (4) the enteritidis group contain bacilli which are 

 motile, which only ferment glucose, and which do not hquefy gelatine 

 or curdle milk, which is ultimately rendered alkahne. This group 

 includes B. enteritidis of Gaertner, the para-colon and the para- 

 typhoid baciUi. 



Streptococci in Water. — Houston considers the presence of strepto- 

 cocci in water as indication of recent and dangerous pollution of 

 water. They are absent even in large quantities of pure water and 

 in virgin soils.t Streptococci, as a class, are delicate germs that 

 readily lose their vitality and die when the physical conditions are 

 unfavourable, and they comprise species highly pathogenic to human 



* Medical Supplement to Report of Local Oovernment Board, 1898^99, p. 498. 



t See also Jour, of Hyg., 1902, p. 339 (Savage). 



X Report of Local Government Board, 1899-1900, p. 483. 



