Further observations on the variability of streptococci in relation to certain fermentation tests, together with some considerations bearing on its possible meaning

The fermentation tests devised by Mr. H. Gordon (1905, 1) were employed by him and by a number of subsequent observers as a means of differentiating streptococci into definite varieties. This application of the tests necessarily presupposes the stability of the reactions yielded by any given strain of streptococci in the test media. But after a prolonged examination of a number of different strains of streptococci I was unable to confirm this primary requirement. Consequently, I ventured to call in question the supposed constancy of the tests (1910,2; 1911, 3). A considerable mass of evidence of the variability of streptococci under cultivation in respect of their reactions in “Gordon’s media” was submitted. The observations recorded made it clear that the reactions in these media of a series of selected strains of streptococci varied independently from time to time under the conditions of ordinary laboratory cultivation, and could in certain cases be made to vary very greatly by growing the organisms for longer or shorter periods in media containing particular “sugars.”