1. The unsaturated fatty acid fraction (OX) from the liver of irradiated rabbits contains substance which has the same effects as X-ray irradiation on the testicular cells. 2. This substance introduced intravenously causes the degeneration of the germinal cells with the formation of giant cells or multi-nucleated cells and the mitotic abnormalities. 3. The DNA content of the cell also shows the changes exactly identical with that seen after X-ray irradiation. 4. From these results we conclude that the X-ray injury will be mainly due to the production of some toxic substance which is found in the unsaturated fatty acid fraction and severely affects the cells in mitosis and DNA metabolism.</p
