DYSENTERY AND ALLIED BACILLI 5 



Thus B. dys. Shiga and B. ambiguus may be distinguished from the others 

 (B. flexneri, B. alkalescens, and B. dispar) by the inability of the former to give 

 acid from the alcohol mannitol. They differ from each other in that B. ambiguus 

 forms indol and ferments rhamnose. 



B. flexneri may be differentiated in a large proportion of instances from 

 B. alkalescens and B. dispar by the reaction in glycerol and xylose. None of 

 the Flexner strains produced acid from xylose, whereas this substance was fer- 

 mented vigorously by 21 of 23 strains of B. alkalescens and B. dispar. Differ- 

 entiation by glycerol fermentation was not so distinct, as a number of the 

 Flexner strains produced a small amount of acid. Quantitative studies showed 

 that this acidity was never beyond the true neutral point PH 7.0. in 5 days. 

 With the indicator employed, however, the results might be confusing in 

 inexperienced hands. 



B. flexneri differs also from B. alkalescens and B. dispar in the milk reac- 

 tion. The former produces a faint acidity in litmus milk, which reverts very 

 slowly, if at all, to a neutral reaction in from 10-13 days. B. alkalescens, on 

 the other hand, reverts relatively rapidly, from 4-8 days, to a distinct alkaline 

 reaction, while B. dispar becomes progressively more acid, eventually coagu- 

 lating the medium. Unfortunately the milk reaction has not given concordant 

 results in the hands of different observers, many recording distinct alkalinity 

 and others coagulating with true dysentery strains of B. flexneri type. 



It remains to differentiate B. alkalescens from B. dispar. The milk reac- 

 tion has been referred to. The objectionable features of this rea'ction are the 

 variability of different batches of milk and slowness of the test. The lactose 

 fermentation of B. dispar, although distinct, is often long-delayed. Table 1 

 shows that although there is some overlapping, the two organisms are markedly 

 different when groups of characters rather than single reactions are considerel. 

 Thus B. alkalescens does not form acid from lactose, sucrose or raffinose, 

 but attacks dulcitol vigorously, while B. dispar rarely ferments dulcitol, but 

 does form acid from lactose and most always from sucrose (81.8%) and 

 raffinose (91.9%). B. alkalescens seems to be a very homogenous group. 

 B. dispar probably consists of several varieties. The indol-negative, 'xylose- 

 negative variety of B. dispar corresponds culturally to the strain isolated by 

 Sonne in Denmark. 



VARIETIES OF B. FLEXNERI 



A number of subdivisions of the mannite fermenting dysentery strains on 

 serologic and biochemical reactions have been proposed in the past. The 

 probable untenability of B. dys. Y as distinguished from B. dys. Flexner has 

 already been referred to. The differentiation of B. flexneri by the English 

 War Committee as determined by careful absorption tests into V, W, X, Y 

 and Z races appears much more acceptable and desirable. 



The value of differentiation of this group on fermentation reactions has 

 fallen into disrepute of late. Thus the fermentation of maltose, sucrose and 

 dextrin, which were formerly emphasized as differentiating varieties of mannite 

 fermenting dysentery strains, is about to be discarded. Maltose was not 

 employed in this study as it was considered unreliable on account of the 

 difficulty in obtaining a product entirely free from glucose, and the ease with 

 which it decomposes on sterilization. Of the tests tried with 59 strains of 

 B. Flexneri the following positive results were obtained with substances that 

 might be of value for subdivision : sucrose, 64.4% ; dextrin, 40.% ; rhamnose, 

 16.9%; raffinose, 79.7%; and indol, 83.1%. The correlation coefficients for each 



