404 TYPHOID FEVER 



GENERAL REVIEW OF THE COLI-TYPHOID BACILLI. 



A general view of the organisms belonging to the coli-typhoid 

 group which we have now considered indicates a close alliance 

 between the various members. All are microscopically indis- 

 tinguishable from one another, and react negatively to the 

 Gram stain. The chief sub-groups can be differentiated by 

 culture reactions, of which the action on sugars is most important. 

 Here important information is obtained by the study of the 

 glucose and lactose reactions. The typhoid sub-group produces 

 acid on glucose, but has no action on lactose. The dysentery 

 sub-group is similar, but is chiefly marked off from the typhoid 

 sub-group by its relative non-motility, by its tendency to form 

 alkali after a preliminary acid development on litmus milk, and 

 by the fact that it does not ferment sorbite. The food-poisoning 

 sub-group is differentiated from the typhoid sub-group by 

 forming acid and gas in glucose and from the coli sub-group by 

 its producing no change on lactose. The positive features of the 

 coli sub-group are the formation of acid and gas in both glucose 

 and lactose. 



From work done not only with bacteria isolated from patho- 

 logical 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 fermenters " from one 

 another. Here the work of MacConkey may be taken as con- 

 stituting one of the best attempts at such further classification, 

 and it has the merit of simplifying a technique unduly compli- 

 cated 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 fermenters in reality give little information. These are, 

 first, the growth on litmus whey, observation of which only 

 corroborates what is observed with litmus milk ; second, observa- 

 tion 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 different 



