From these data it is seen that ill defined divisions of the so called Flexner group exist. The divisions do not appear to be sufficiently distinct to warrant the use of separate names. To avoid confusion all mannitol-fermenting dysentery bacilli should be called Bacillus dysenteriæ Flexner and the subdivision noted. There are two methods for this division, one by the fermentation of carbohydrates, the other by agglutination with monovalent rabbit sera. These do not coincide and one or the other and not both must be adopted. Inasmuch as Murray studied organisms from widely distributed sources, it would seem preferable to adopt his serological classification and to add to it the types that fail to be agglutinated by his V, W, X, Y, and Z sera, as this method is simpler and more rapid. The results of the agglutination reactions of the patient's serum may be expressed in the same terms as the serological typing of the organism from his stool. Fermentation is less constant and gives rise to more divisions than there are carbohydrates.

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The serological reactions of these type sera, as Murray points out, show cross-agglutination to a greater or less extent, but they indicate that there are five antigens, V, W, X, Y, and Z and probably others, one or more of which predominate in a given strain. Polyvalent diagnostic and therapeutic sera are practically worthless unless they include antibodies for the more common of these types.

The diagnostic importance of recognizing that there are five or more antigens in this group is seen from the fact that the sera of some patients react with one, others with another, and that unless several antigens are used, some positive tests may be missed.

The therapeutic importance is emphasized by the fact that probably the best polyvalent therapeutic serum at present available has a very low titer for the X antigen, although that type was found in many of these cases (Table V).

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