392 TYPHOID FEVER 



the inconstancy of the occurrence of this change in lactose 

 fermenters, and from the fact that many other bacteria also 

 produce it) ; third, the reduction of nitrates, this appears 

 to be a common property of nearly all the members of the 

 group ; fourth, observation of differences in the naked eye or 

 low power appearances on gelatin ; these are very inconstant, and 

 different colonies of the same organism may show different 

 appearances. On the other hand, important information may 

 be obtained by the observation of the Voges and Proskauer 

 reaction (p. 353). With regard to sugars, McConkey concludes 

 that in the differentiation of the lactose fermenters, the only 

 sugars necessary are lactose, saccharose, dulcite, adonite, inulin, 

 inosite, and mannite. Using these, a preliminary classification 

 can be made from the actions on cane-sugar and dulcite, and 

 four groups are constituted : I. Organisms not affecting either 

 cane-sugar or dulcite. II. Organisms having no action on cane- 

 sugar, but fermenting dulcite. III. Organisms fermenting 

 both cane-sugar and dulcite. IV. Organisms fermenting cane- 

 sugar but having no action on dulcite. Of the first, the 

 bacillus acidi lactici of Hiippe may be taken as a type ; 

 of the second, the bacillus coli communis of Escherich ; 

 of the third, bacillus Friedlander ; of the fourth, the bacillus 

 lactis aerogenes and the bacillus cloacae. Group IV. is further 

 sub-divided into sub-group 1, in which there is no lique- 

 faction of gelatin and an absence of the Voges and Proskauer 

 reaction ; 2, with no liquefaction of gelatin, presence of Voges 

 and Proskauer's reaction (bacillus lactis aerogenes) ; 3, with 

 liquefaction of gelatin, presence of Voges and Proskauer's 

 reaction (bacillus cloacae) ; 4, with liquefaction of gelatin and 

 production of a yellow pigment. Taking the properties named 

 as type characteristics, the great mass of lactose fermenters can 

 be further differentiated by the application of the other sugar 

 tests. It is well to refer any organism found as belonging to 

 one or other of the types, as in most cases no name has been 

 assigned. Examples are constantly met with in work on water 

 or faecal contents. 



Although many of the named varieties were originally 

 described in connection with other bacterial processes, all these 

 bacteria are of frequent occurrence, especially in the human and 

 animal intestine. As in the case of the members of the food- 

 poisoning group, great difficulty has been experienced in 

 identifying the types from mere description, and considerable 

 complication has arisen from the fact that before the elaboration 

 of the modern differentiation technique, different observers 



