Studies in Bacterial Variability. 



65 



The bouillon culture (A) of which T. dys. was an immediate subculture had 

 been plated out on agar as already mentioned. From these plates 20 colonies 

 were picked off into bouillon on each of the succeeding 3 days. They were 

 incubated for 24 hours, and then examined for motility and formolised for 

 agglutination tests. All these 60 cultures were highly dys-agglutinable, and 

 they were all non-motile, with the exception of one out of the third set of 20. 

 This culture which, it will be noted, had grown for 5 days on serum-free 

 media and had been three times subcultivated (once on agar and twice in 

 bouillon), had begun to revert, and showed a certain proportion (possibly as high 

 as 20 per cent.) of motile individuals among the mass of non-motile elements. 

 It is interesting to observe that this proportion of motile elements was not 

 sufficient to render the culture eu-agglutinable. 



So far, then, as the evidence from the bouillon subcultures of sixty 

 colonies goes, the original T. dys. culture consisted entirely of non-motile 

 bacilli. 



It is not necessary on the present occasion to go into much detail in 

 describing results which showed increase of agglutinability o.nd the occurrence 

 of hyper-agglutinable forms. 



The culture T.e. 9 exhibited a degree of hyper-agglutinability. It was 

 about two and a half times as agglutinable by standard serum as T.e. or T. 36, 

 Furthermore, the culture T. 36, with which it was compared, was itself a 

 highly agglutinable culture. It had an index of 7, that is to say, it was 

 nearly three times as agglutinable as the original standard agglutinable culture 

 on which Dreyer's unit was chosen, whose index was 2*5. If, as I suggest, 

 this original standard be taken as the mean standard of eu-agglutinability r 

 the culture T.e. 9 was seven times as agglutinable as that standard, and may 

 be regarded as distinctly hyper-agglutinable. In further experiments, a 

 still more highly hyper-agglutinable culture (about twice as agglutinable as 

 T.e. 9) was readily obtained by growing the bacillus in serum bouillon, 

 centrifugalising out the flocculent clumps at an early stage, and making the 

 succeeding serum bouillon culture from the deposit, and so on, instead of 

 working from the supernatant fluid, as in the pursuit of dys-agglutinable 

 forms. 



Similarly, starting from a dys-agglutinable culture, one can frequently 

 restore it to eu-agglutinability by the same procedure. Needless to say, all 

 these operations demand rigorous precautions against accidental contamina- 

 tion of the cultures. The method has a practical application which deserves 

 mention. 



Strains are sometimes met with in the case of B. typhosus (and the same is- 

 true of a number of other bacteria), which are <: bad agglutinators." Or it 

 vol. xcni. — b. F 



