With a molybdenum tube run at 50,000 volts, a dose of 60,000 e, equivalent to 3 microcoulombs in the electroscope, invariably proved fatal; while smaller doses elicited certain characteristic responses and also produced a delayed effect often causing cell division. A temp. rise of 3[degree]C. was produced in the culture resulting from the radiation, but this could have no bearing on the results. Assuming that the ionization of one of the molecules of a given structure in the cell is sufficient to constitute a "hit," and that all the "hits" are made on the same structure, an equation is developed giving the relation between the number of individuals surviving and the constants of the exposure. The survival curves have the shape predicted by the theory. It is possible to deduce the size of the structure affected by the radiation and responsible for the death of the organism. Under the assumptions given, if the structures were spherical it would have a diam. of 3.5 X10-5 cm. Or, assuming that only the more violent processes constitute a "hit" and that each high speed electron produces 1000 pairs of ions in its course, the diam. of the structure may be as large as 3.5X10-4 cm.