[' ', 'Mouse', 'skin', 'is', 'the', 'only', 'experimental', 'material', 'known', 'be-', 'yond', 'doubt', 'to', 'respond', 'to', 'continued', 'application', 'of', 'cigarette-smoke', 'condensate', 'with', 'the', 'formation', 'of', 'papillomas', 'and', 'carcinomas.', 'While', 'mouse', 'skin', 'is', 'far', 'removed', 'from', 'the', 'bronchial', 'epi-', 'thelium', 'of', 'man,', 'it', 'is', 'at', 'present', 'the', 'only', 'practical', 'system', 'for', 'com-', 'parisons', 'of', 'carcinogenic', 'potency', 'of', 'cigarette~smoke', 'condensates.', 'It', 'is', 'the', 'only', 'logical', 'test', 'system', 'for', 'cosmetics', 'and', 'other', 'sub-', 'stances', 'that', 'exert', 'their', 'effects', 'through', 'dermal', 'contact.', 'According', 'to', "Berenblum's", 'views,', 'which', 'have', 'found', 'wide', 'ac-', 'ceptance', 'among', 'cancer', 'researchers,', 'there', 'are', 'atleast', 'two', 'classes', 'of', 'substances', 'involved', 'in', 'carcinogenesis,', 'i.e.,', '(1)', 'carcinogens', 'proper,', 'or', 'initiators,', 'which', 'cause', 'tumors', 'when', 'administered', 'alone,', 'and', '(2)', 'cocarcinogens,', 'or', 'promoters,', 'which', 'are', 'noncarcinogenic', 'when', 'applied', 'alone,', 'but', 'which', 'increase', 'significantly', 'the', 'rate', 'of', 'tu-', 'mor', 'formation', 'caused', 'by', 'very', 'small', 'doses', 'of', 'carcinogens', 'admin-', 'istered', 'previously', 'or', 'simultaneously.', 'Mouse.', 'skin', 'painting', 'permits', 'the', 'study', 'of', 'both', 'types', 'of', 'phe-', 'nomena:', 'tumor', 'initiation', 'and', 'tumor', 'promotion.', 'Carefully', 'planned', 'skin-painting', 'experiments', 'make', 'pos-', 'sible,', 'for', 'example,', 'quantitative', 'evaluation', 'of', 'carcinogenic', 'and/or', 'cocarcinogenic', 'potency', 'of', 'smoke', 'condensates', 'or', 'their', 'fractions.', 'The.', 'method', 'is', 'not', 'limited', 'to', 'tobacco', 'and', 'smoke', 'products', 'and', 'is', 'also', 'applicable', 'to', 'the', 'study', 'of', 'other', 'types', 'of', 'compounds', 'sus-', 'pected', 'of', 'being', 'carcinogenic', 'or', 'cocarcinogenic.', 'Bio-Research', "Consultants'", 'experience', 'with', 'mouse', 'skin', 'painting', 'The', 'first', 'skin-painting', 'study', 'carried', 'out', 'in', 'our', 'laboratory', 'was', 'done', 'in', '1960-1962', 'and', 'published', 'in', '1963', '(J.', 'Nat.', 'Cancer', 'Inst.', '31:', '1455-59,', '1963).', 'Ever', 'since', 'then,', 'without', 'interruption,', 'one', 'or', 'more', 'projects.on', 'skin', 'painting', 'have', 'been', 'in', 'process', 'in', 'this', 'labora-', 'tory.', 'The', 'data', 'obtained', 'inthese', 'studiesare', 'the', 'property', 'of', 'several', 'clients', 'and', 'have,', 'therefore,', 'not', 'been', 'published.', 'COPrpretooer']