(Fram theInstituto Quimio-Biologico,Camcas,Venezuela) (Receivedfor publkation AuguS't9, 1946)

significantaugmentationof the incidence of pulmonary adenomasof mice of the C3H straintreatedby repeated inj ectionsof ethyl urethane. Henshaw and Meyer (1) confirmed this observatiémworking with mice of the abc strain, which has a high spontaneousrate for tumors of this type. These authorshave shown that the incidence of adenomasproduced by the injection of urcthane dependson the amount applied, and con-cludcd that a single nonanestheticdose is suflicient to produce someeffect. Larsen and Heston (5) studied a numbcr of narcotics with respect to their carcino-genic action. Only ethyl urethane and some other urethane derivativeswere found to produce pulmonary adenomasin mice. We havefound that ethyl urethane applied by injection or by mouth produced pulmonary adenomasin our noninbred strain of mice, which has a relatively low spontaneousincidence of lung adenomas (4). The action was very marked when the active substancewas injected or given orally. Each author confirmed the high degreeof specificityof urethanein producing only pulmonary adenomas,since no other type of tumor hasbeen observedin the treatedmice. As pulmonary adenomaof mice is a specialkind of relatively benign tumor, which very frequently occurs spontaneously,it seemedof particularinterestto investi-gate the action of urethaneon an animal specieswhich does not develop this kind of neoplasticgrowth spon-taneously. For this purpose rats seemed especially suited, as they seldomdevelopspontaneouslung tumors (2). The resistanceof rat lung tissueagainstdevelop-ment of tumorshas been shown also in experimentsin which carcinogenic hydrocarbonshave been injected intravenously. R. J affé (3) found only 2 pulmonary sarcomasin 90 rats injected intravenouslywith an oily solution of methylcholanthrene,while 3Oper cent of the animalshad tumors in someother site. lt thereforeseemedof interestto investigatethe car-cinogenic actioh of urethaneon rats. lf the action of this substanceis as specific as the results with mice seemedto indicate, it was hopcd that somc reaction of rat lungs would be produced which does not occur spontaneously.