In the freshly emitted luminous slime of M. phosphoreus 2 kinds of granules occur, one of which dissolves with light production, if water is added, 2nd remaining intact. Many observations indicate that these 2 kinds of granules represent but the different stages of the same kind of bodies. Osmotic pressure and the action of different ions have no effect on dissolution and luminescence of the luminous material. If water is not present in sufficient quantity, the luminescence is suppressed reversibly. Agents such as HgCl2 destroy the power of luminescence irreversibly.