34 MILK AND THE PUBLIC HEALTH CHAP. 



also contains bacilli differing in more or less important 

 characters from this particular organism. 



From the point of view of the application of our knowledge 

 of the bacteriology of milk to practical purposes, R coli and 

 allied forms are of significance only as far as they are them- 

 selves organisms of definite pathogenicity, or in so far as they 

 are indicators of undesirable pollution of the milk. 



The significance of this group in milk bacteriology and the 

 inter- relationship of the different bacilli may be considered 

 from two points of view : the practical and the strictly 

 scientific. 



We may, on the one hand, define the group widely enough 

 to embrace all the varieties which are either themselves 

 harmful or indicators of outside pollution, or we may subdivide 

 up the group, by introducing a large series of tests, into a large, 

 almost an indefinite, number of varieties, and try to ascertain 

 the exact distribution in nature of each variety, and measure its 

 precise significance either as a potentially pathogenic bacillus 

 or as an indicator of some definite kind or kinds of pollution. 

 The latter plan is undoubtedly the more scientific and logical, but 

 the knowledge of this group and the distribution of the different 

 sub-groups is at present scarcely sufficient to make it a pro- 

 cedure of immediate practical value. 



MacConkey has given great attention to the further 

 differentiation of the lactose fermenting bacteria of intestinal 

 origin. In his opinion, many of the classical tests for B. coli 

 and allied organisms do not permit of adequate differentiation 

 of the lactose fermenting bacilli. He proposes * to omit growth 

 in litmus milk, on gelatine slope, the fermentation of glucose, 

 character of the growth on gelatine, production of fluorescence 

 in neutral red, etc., and to lay great stress upon certain fer- 

 mentation tests. The tests he suggests should be used are 

 the following : 



The presence or absence of motility, the fermentation of 

 lactose, saccharose, dulcite, adonite, inosite, inulin, and possibly 

 mannite, the production of indol, and Vosges and Proskauer's 

 reaction. 



With these tests, he believes we shall be able to pick out 

 those organisms which are most closely associated with faeces. 



1 Joum. of Hygiene, 1909, ix. p. 86. 



