The preceding studies on carcinogenesis (Shear, 1936, a, b) dealt with the production of tumors by hydrocarbons related to 1:2-benzanthracene. The finding of Kennaway1 and his colleagues that hydrocarbons are carcinogenic was the culmination of a search for the active agent in coal tar which began when Yamagiwa and Ichikawa (1915) announced the experimental production of skin tumors with coal tar. The success of these Japanese investigators was, in turn, the outgrowth of numerous attempts on the part of many previous investigators to induce malignancy in experimental animals by the administration of a wide variety of substances. Among the substances used by Yamagiwa and Ichikawa (1915, 1918) in attempting to produce malignant growths was scarlet red; this was used alone and in combination with tar. Hyperplasia was produced by scarlet red but, for various reasons, its use was discontinued and coal tar was used alone. Scarlet red was also injected into the wall of hens' oviducts by Yamagiwa and Ohno (1918) in an attempt to produce glandular cancer; carcinoma was obtained in 3 of the 41 hens, and hypertrophy in many others. One tumor contained scarlet red in the center of the neoplasm. This use of scarlet red originated with B. Fischer (1906). After testing many substances in earlier attempts to produce malignant growths, he injected a solution of scarlet red into the ears of rabbits. The atypical epithelial proliferation which resulted was difficult to distinguish, histologically, from cancer, but the growths always receded. Fischer stated that this was the first instance in which tumor-like proliferation had been produced by a chemical compound, and suggested that this finding threw a new light on the genesis of malignant growths, especially on the genesis of paraffin cancer, chimney sweeps' cancer, and similar occupational cancers.