Tar Epithelioma in the Sympathectomlzed Albino Rabbit

Abstract

Occupational tar cancer, or the development of malignant epithelial tumors in those whose work entails prolonged exposure to tar or to certain closely related substances, has for many years constituted a recognized clinical entity. The close causal relationship between chemical agent and tumor development apparent in these cases has stimulated numerous attempts during the last forty years to produce analogous new growths under experimental conditions. These attempts did not prove successful, however, until 1915, when Yamagiwa and Itchikawa (1) as a result of combining the factors of adequately prolonged exposure, potent carcinogenic agent, and susceptible species of experimental animal, were able to report the development of carcinoma in the rabbit's ear following the repeated application of coal tar. This major experimental advance, facilitating the study of a form of neoplasia under conditions controlled at will in the laboratory, has evoked extensive experimental investigation which has added greatly to our knowledge of the nature of tumors. The results of tar cancer experimentation were comprehensively reviewed in 1926 by Woglom (2). Among the factors which lend themselves readily to experimental control in the investigation of tar tumors is the influence of nervous supply from the sympathetic system. The present paper, based upon study of a group of thirty albino rabbits, reports the incidence and course of tar epithelioma as observed in the sympathectomized and in the normal ear. Method Healthy albino rabbits were used for the experiment, especial care being employed in their selection to ensure absence of scarring or other lesion of the ears. Initial weights ranged from 4 to 7 pounds. Selection of subjects was made without regard to age or sex. The tar used in this experiment was prepared from a residue kindly furnished by Dr. James B. Murphy and previously shown by him to be of high carcinogenic potency for mice. This residue was produced in a coke oven in which the tar had been distilled at a temperature of approximately 377° C. The tar was obtained by a process of extraction and purification similar to that described in 1925 by Murphy and Landsteiner (3).