Studies in bacterial variability.— On the occurrence and development of dys-agglutinable, eu-agglutinable and hyper-agglutinable forms of certain bacteria. (A report to the medical research council.)

That different cultures of an agglutinable bacterium may exhibit wide differences in relative agglutinability when tested with the same agglutinating serum is a familiar fact. But the conditions on which these differences depend remain to a great extent obscure. Yet a number of facts which bear upon the problem have come to light in the course of investigations carried out by various observers. A good many years ago the present writer showed (1901) (1) that if a series of strains ofB. typhosus be employed in preparing a corresponding series of agglutinating serums, each such serum is found to act more powerfully upon its homologous culture than upon any of the heterologous strains. It was, therefore, stated that the serums were not only specific for the species of bacterium in question, butalso special in each case to the particular strain employed in its production. It also appeared that, so far as the evidence went, the heterologous strains always fell into the same order of relative agglutinability when tested with the different “special” serums.