E VER since the demonstration in 1930 by Kennaway and Hieger that I , 2 , 5,6-dibenzanthracenc, a pure chemical compound, is capable of producing cancer, there has been a great deal of interest and work in the field of chemical carcinogenesis. The isolation and characterization of 3,4-benzpyrene as one of the carcinogenic agents of coal tar by Hieger13 and by Cook and Hewett, in 1933, stands as one of the milestones in this field, and tied in the researches on occupational skin cancers with the ever-increasing activity in the study of the carcinogenic hydrocarbons. This work was carried on chiefly by Cook and Kennaway in England and Fieser and Shear in America, by whom a very large number of related compounds were synthesized and tested for carcinogenic activity. As the synthetic activity was at its height, a series of investigations were launched with the aim of elucidating the mode of action of these substances. This work has mostly been concerned with the three compounds, I, z,5, 6-dibenzanthracene, 3,q-benzpyrene, and 2 0methylcholanthrene, and centered about studies of the distribution, metabolism, and effect of these substances on the biochemical and physiological environment of the cell, epidermis, and the animal as a whole.
The analytical technique that has been em-