A New Suspending Medium Used for the Intracutaneous Virulence Test of Bacillus Diphtheriae

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Abstract
Morphology as determined by smear examination of diphtheria cultures offers no true evidence as to virulence of strains. Various virulence tests discussed (including cataphore-sis) are either uncertain or impractical. The intracutaneous test is practicable but has been shown by the authors to be subject to inaccuracy. Pure cultures, particularly, do not induce local necrosis. A suspending medium overcomes this, and intradermal tests of a series of strains so suspended compared very favorably with actual toxicogenic properties of these same strains in vitro. The formula for this suspending medium is given. It is sterilized at 15 lb. pressure for 30 min., after tubing, 1 cc. per tube; tubes are corked and sealed with paraffine. Care must be taken to prevent evaporation of the stored suspending medium, since a very slight further concentration increases the percentage of agar sufficiently to solidify the fluid. Different lots of shredded agar vary in "setting" property; each new lot should be tested.