The report of Marbe and Olariu showing that a good yield of toxin could be obtained on a medium containing only Proteose-Peptone, Bacto-Peptone, maltose, dextrose and sodium acetate has been confirmed.
A study has been made of the suitability of other peptones for use in such a medium. Protone and proteose-peptone No. 2 have been found to yield good diphtheria toxin when substituted in the Marbe and Olariu formula. Neopeptone has been found to be very poor and tryptone and yeast-extract have been found to be worthless when used in the formula in the concentrations studied.
Of all the concentrations and combinations used, a 4 per cent solution of peptone composed of 1/3 proteose and 2/3 proteose-peptone No. 2 has been found to give the best and most consistent yields of toxin.
A complete dried medium is described, which when dissolved in cold water to a concentration of 5.8 per cent, dispensed in 700 ml. amounts in 2-gallon Blake bottles, autoclaved and inoculated gives a good yield of diphtheria toxin (20 to 26 Lf per milliliter) with the preparations and culture tried.