FOOD-POISONING BACILLI 393 



less colonies which can be picked off for systematic investigation. 

 In the case of blood, ordinary methods will prove sufficient. 



Capacity for fermenting sugars has been largely applied in 

 work on this group. All the members produce practically the 

 same reactions. They originate acid and gas in glucose, laevu- 

 lose, sorbite, inannite, dextrin, maltose, dulcite, galactose and 

 arabinose, like b. coli, but produce no change in lactose, raffinose, 

 cane-sugar, salicin or inulin. Of these the actions on lactose and 

 dulcite are most important, as the former differentiates the group 

 from b. coli and the latter from b. typhosus and b. dysenterise. 

 Although differences in fermenting capacity have been noted in 

 different strains, the existence of such cannot be relied upon for 

 differentiating members of the group from one another. The 

 sugar reactions are only of use in demarcating the lines between 

 the food-poisoning group and b. coli on the one hand, and b. 

 typhosus on the other. The differentiation of members of the 

 group can only be effected by applying serological tests to the 

 serum of animals suffering from natural or artificial infection. 

 The chief point here is that in such infections the occurrence of 

 group agglutinins in the serum is much in evidence. Herein lies 

 the necessity for having at hand the historic strains of the 

 organisms referred to above. In dealing with an organism, it is 

 first of all advisable to take the serum of the infected individual, 

 estimate the highest dilution with which it clumps the strain 

 isolated, and compare the result obtained with the effect of the 

 serum on the historic strains. The unknown strain is most likely 

 to be allied to that strain which is agglutinated by a similar 

 dilution of the serum used. Frequently, in the investigation of 

 an organism, it is necessary to inject it into an animal and study 

 the agglutinating properties of its serum on the infecting strain 

 and upon allied organisms. Here the most reliable information 

 is obtained by the use of the absorption method. If from such 

 a serum, for instance, an unknown organism has absorptive 

 qualities similar to that of a historic Gaertner, its being named 

 a Gaertner bacillus would be justified. If a series of immune 

 sera against different members of the group is available, the 

 serum which agglutinates an unknown organism in highest 

 dilution may be determined. The organism may then be 

 identified with that with which the serum was produced. It is 

 customary in any case to note the action of a typhoid serum on 

 an organism under investigation, and also the action on the 

 typhoid bacillus of an antiserum to the unknown organism. 

 Leuchs, Altmann, and H. R. Dean have successfully applied 

 the method of complement fixation to the differentiation of the 



