[en] The problems involved in chemical mutation work are both complex and varied. With ionizing radiation it is known that genetic effects are produced in all organisms, in all cells, and the assessment of genetic risk is thus one of ascertaining how much damage is being induced: It is a quantitative problem. By contrast, chemical mutagens may be highly mutagenic in one organism, or one cell type, but totally ineffective in another. In cases where mutagenic effects are produced, all those classes of mutation recovered following radiation may occur, or only a few. Where no mutagenic effects can be detected, this may be due to any one of a variety of different causes