Abstract
Having bronchial epithelium theory and alveolar epithelium theory, opinions of various workers on the above subject has yet not come to the conclusion. The author conducted various investigations on the lung tumors induced in mice by the oral administration of 0.1% urethane. The following results were thus obtained.
(1) The greatest majority of the cases (102 out of 105 tumors) was alveolar epithelial. Nevertheless, though small in number (3 out of 105 tumors), bronchial apithelial tumors were definitely recognized.
(2) The existing theory that the tumors frequently induced subpleurally is the result of superficial observations. Actually, no significant difference was recognized between the two.
(3) Inflammation and atelectasis showed no particular causative relations with the formation of the tumors.
(4) As far as the experimental results over a period of 28 weeks, no malignant tumors have not yet discovered.
