THE purpose of the experimental work reported in this manuscript is to demonstrate a possible mechanism whereby tar and other combustion products in cigarette smoke might be deposited in the lower respiratory tract of human beings. An impressive body of literature has accumulated to support the thesis that prolonged and heavy cigarette smoking is positively related to the increased incidence of bronchogenic carcinoma. These reports are of three general types: statistical studies; post-mortem examinations of the bronchial epitheliums of smokers versus nonsmokers; and experimental data on the carcinogenicity of the combustion products of tobacco.

In May, 1950, Wynder and Graham . . .