An earlier study having established that (1), as soon as the detoxification of diphtheria toxoid is complete, the formalin can be eliminated by precipitation with acetone without apparent injury to the toxoid, further experiments were undertaken to determine the most suitable concentration of formalin and period of exposure when the preparation was incubated at from 36 to 37°C.

The preparation of diphtheria toxoid by the methods of Glenny (2) and of Ramon (3) involves prolonged incubation at elevated temperatures and with minimal quantities of formalin, from 0.3 to 0.4 per cent, so carefully adjusted that, when detoxification has reached the desired stage, changes affecting the antigenic action will not take place. There are obvious advantages in avoiding this complicated procedure and in adopting one that would eliminate the formalin as soon as the product was satisfactorily detoxified.

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