more, Shiga claims by immunizing animals to have produced a serum which has reduced the mortality in " epidemic " dysentery in Japan from about 35 per cent, to 9 per cent.
The cultural characters of B. dysenteriœ are subject to great variation. As a consequence considerable confusion has arisen; but it is now generally conceded that, though indicating different strains of bacilli, these differences are not specific. The Table which will be found on p. 509 indicates the leading characters of the various strains and a comparison with other pathogenic intestinal bacilli.
Many strains of B. dysenteriœ have been described, and though all resemble each other in their gross cultural characters on solid media, etc., yet they differ considerably from each other in their chemical reactions with solutions of various sugars and in their production of indol. Thus Ohno has described over fifteen varieties, but more recent work indicates that there are probably nothing like this number, and that many of the sugar reactions not only vary according to the length of time of subculture, but even from day to day for given strains of the bacillus. On only one point is there universal agreement, and that is in the property possessed by bacilli of the acid or Flexner group of producing acid from mannite, and the lack of acid production in this sugar by the non-acid or Shiga group. Shiga now recognizes five types which he uses for the production of polyvalent anti-serum in Japan. These are:
- (1) Fermenting dextrose alone (Shiga-Kruse). '
- (2) The true Flexner bacillus, fermenting dextrose and mannite and saccharose.
- (3) The " Y " bacillus, fermenting dextrose and mannite.
- (4) Fermenting dextrose, maltose, and saccharose.
- (5) Fermenting dextrose and maltose, but giving only a feebly acid reaction with mannite.
There is also great variation in the toxicity of various strains of bacilli, especially after long subculture on artificial media. The serum of an animal injected with one strain will agglutinate bacilli of another in high dilutions. Even the serological tests of patients suffering from dysentery caused by one type of bacillus give uncertain results. Penfold and others have shown that cultural reactions which are constant for one type of bacillus can be made to vary by growing the same bacillus under different conditions, and even passage through the intestinal tract of a fly may exert a temporary influence on their power of fermentation (Bahr). The three main types of bacilli now recognized are the Shiga-Kruse, the Flexner, and the bacillus of Hiss and Russel. (See Table on p. 509.)
