Susceptibility of newborn mice of resistant strain to chemical cancerogen.

quarter was regulated between 18? and 25•Ž. Incidence of lung tumor among thus treated mice was very high at the age of 3 months exceeding 75%. Whereas, among the untreated controls and mice administered the identical agent or subcutaneous injection of methylcholanthrene-rosin pellet2) 30 days after birth the incidence was very low and retarded, not exceeding 1 % and being detected after 8 months. Numbers of animals examined so far are too small to determine exact percentages and time of onset of tumor formation at this time. Tumors observed were histologically identical in all groups ; that is, benign papillary adenocarcinoma,3) presumably of alveolar origin. However, a tendency was noticed in the group treated at 30 days to form a single tumor mass at the caudal