394 TYPHOID FEVER 



to be the case if tie two organisms are clumped by approxi- 

 mately the same dilution of the serum. On this principle is now 

 based the ultimate determination of the species to which a 

 strain isolated by culture belongs. It is usually applied im- 

 mediately after the organism has been classified into its cultural 

 group by. its. behaviour towards mannite and by the presence or 

 absence of motility (see p. 389). In the use of- the test, high- 

 titre sera obtained by the immunisation of animals with historic 

 or otherwise reliable strains are employed. The observer must 

 be provided with sera against the b. typhosus, b. paratyphosus 

 A, b. paratyphosus B, b. gaertner, b. dysenteriae, Shiga, and 

 b. dysenteries Y (the latter is used as it agglutinates a large 

 number of Flexner strains which, on account of their dominant 

 individuality, do not readily yield cross-agglutinins towards each 

 other) ; the titre of each serum to the strain which produced it 

 must be known. In the diagnosis of bacterial strains the 

 sedimentation method should be employed. 



In any extended investigation of intestinal infections bacilli 

 will be met with not agglutinable by any sera which on the 

 cultural data seem to be appropriate to them, and yet the con- 

 ditions of their isolation may point to their etiological connection 

 with the disease with which they are associated. This pheno- 

 menon is at present unexplained. 



Varieties of B. Ooli. 



From work done not only with bacteria isolated from pathological 

 conditions, but in connection with the bacteriology of water, milk, and 

 faeces, it has been found that an enormous number of organisms exists 

 which have the capacity of fermenting glucose and lactose, but which, 

 when further investigated, present individual differences. Much has 

 been done in attempting to differentiate these so-called "lactose fer- 

 menters " from one another. Here the work of MacConkey may be taken 

 as constituting one of the best attempts at such further classification, 

 and it has the merit of simplifying a technique unduly complicated by 

 the use of fermentation tests in a great series of sugars, on which the 

 various sub-groups have all the same effect. MacConkey is of opinion 

 that certain of the tests applied to the lactose fermenterB in reality give 

 little information. These are, first, the growth on litmus whey, observa- 

 tion of which only corroborates what is observed with litmus milk; 

 second, observation of fluorescence on neutral-red lactose media (on 

 account of 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 differ- 

 ent appearances. On the other hand, important information may be 

 obtained by the observation of the Voges and Proskauer reaction (p. 356). 



