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A large number of studies have been made to determine the carcinogenic substance or substances in coal tar. At the present stage of investigation it seems probable that no specific substance can be incriminated. In general, the fraction produced by distillation at high temperature has been found more effective than that obtained at lower temperatures. The residual pitch has been found to be carcinogenic both in man and in animals. This monograph is a study of the carcinogenic properties of the fractions obtained by distillation of pitch, those being selected which are acid, neutral or alkaline. The neutral portion is most active in producing growths in the rabbit, and, of the neutral fractions, those distilling between 200 and 240 degrees at a pressure of 4 mm. were more active than the others, thus confirming in a general way the investigations hitherto made. The text of the monograph is in Japanese,
Study of the Coal-Tar Pitch, with Special Regard to Its Epithelioma-Producing Factor.. JAMA. 1930;95(7):553. doi:10.1001/jama.1930.02720070091034