Observations on Animals Painted with Tobacco Tar

Abstract

The importance, in the etiology of cancer, of various agents, such as roentgen rays (1, 2), radioactive substances (3, 4), ultraviolet light (5), certain animal parasites (6, 7), coal tar (8), and some hydrocarbons (9, 10, 11) which produce prolonged or chronic irritation is now generally recognized. Such studies have not been limited to experimental animals, and a number of writers have suggested a relationship between these agents and certain forms of occupational cancer. The high incidence of cancer of the lip, tongue, and throat in men as compared to the infrequency of such cancer in women has frequently been attributed to persistent irritation of the epithelial surfaces by tobacco tar, to which men have been exposed to a much greater degree. Stimulated by these observations, several investigators have studied the action of tobacco tar and smoke in different species of animals. In 1911, Wacker and Schmincke (12) succeeded in producing an atypical proliferation in rabbits9 ears after application of tobacco tar, obtained from pipes, mixed with crude paraffin oil. Helwig (13) found that the ethereal extracts of tobacco tar obtained from the bowls of briar pipes and combustion products of tobacco distilled over at temperatures between 400 and 500° C. did not contain any carcinogenic substance capable of producing unlimited growth of epithelium in mice. Tobacco tar when mixed with olive oil and injected into the ears of rabbits caused atypical epithelial proliferation, but in no instance did it produce actual malignant transformation. Chikamatsu (14) painted the skin of mice and the ears of rabbits with tobacco tar and found it to be inactive on mice though it caused the development of a cancroid on a rabbit9s ear 225 days after the beginning of treatment.