Studies in Bacterial Variability. 



57 



selection of a character for artificial increase, the other the selection of individuals 

 for multiplication. And it is obvious that both processes might be at work 

 side by side. 



In view of these considerations, it seemed likely that information of interest 

 would be obtained by inquiring what degree of parallelism, if any, existed 

 between the differences in agglutinability to be observed in different strains 

 (however derived), and those obtainable by repeated cultivation in agglu- 

 tinating serum. In particular it was hoped to throw some light on the nature 

 and origin of so-called " serological strains " in different species of bacteria. 

 Accordingly experiments have been carried out as described below. Mean- 

 while the experiments of Gardner and myself already referred to (loc. cit.) 

 have shown that extremely wide differences in agglutinability, such as might 

 well form a basis for either process of selection, do actually exist between the 

 individuals which constitute the population of a single culture. 



In the account which follows, the experimental work has been summarised 

 so far as possible, and detailed data are recorded only for B. typhosus, in 

 order to save space. A general survey of the phenomena under investigation 

 is given, but only a selection of the experiments is recorded in illustration. 

 In certain directions the results are preliminary, and a number of points 

 remain to be worked out in detail. 



The Experimental Production of Dys-agglutinable and Hyper-agglutinable 

 Strains (or Phases) of Bacteria. 



By repeated subculture in specific agglutinating serums diluted appro- 

 priately with culture bouillon, dys-agglutinable forms have been obtained of 

 the following bacteria, ten in all, which were all taken from strains then in 

 use in the department : B. typhosus, B. paratyphosus A., B. paratyphosus B., 

 B. certrycke, B. enteritidis (Gaertner), B. coli, B. dysenterice (Shiga), B. dysenterice 

 (Flexner), V, W and Z. 



On transference from the serum bouillon .to ordinary culture bouillon, 

 these dys-agglutinable forms yield cultures which agglutinate with difficulty, 

 if at all, with corresponding ordinary agglutinating serums ; and those of 

 them that were originally motile organisms are found to have passed into a 

 very feebly motile or entirely non-motile phase. After formolisation and 

 dilution to the opacity of standardised agglutinable cultures, they yielded 

 good and uniform suspensions for agglutination tests, though in a number of 

 cases this result was not obtained immediately or very easily. The dys- 

 agglutinable phase of B. typhosus and of B. dysenterice (Flexner), Y, W and Z 

 readily yielded excellent suspensions on a number of occasions. 



In other cases difficulty sometimes occurred for one of two reasons — 



