The combining power of tetanal toxins, measured in L+, can be doubled by the presence of activated charcoal during the formation of the toxin in peptone-containing media. For the brands of charcoal used, approximately 0.2 per cent was found to be the optimal amount.
A similar effect, but less pronounced, was found if paper pulp or cheesecloth were used in place of charcoal.
In the toxoids tested, (toxoids which correspond to charcoal-toxins and controls prepared in the absence of charcoal) an increased antigenicity was found corresponding to the increase of combining power in the toxin.
The use of activated charcoal has an additional advantage in that it simultaneously removes colored matter from the medium, so that corresponding alum precipitated toxoids are colorless in appearance.