FOUR FIGURES
Recent studies on the effect of ultraviolet radiations upon division rate of sea urchin eggs have demonstrated that less energy is needed at h2804A than at A2654A for equivalent retardation (Giese, '38a). The first wavelength is near the absorption maximum of cytoplasmic proteins (Coulter, Stone and Kabat, '35), the second near the maximum for nucleoproteins (Heyroth and Loofbourow, '33 ; Caspersson, '36). Similar quantitative data on the retardation of cleavage following irradiation of the sperm used to inseminate unirradiated eggs are needed to compare the energy requirement and the wavelength sensitivity of the eggs and sperm. Such data should be especially interesting since the sperm is almost a naked nucleus. An analysis of the effects of ultraviolet radiations upon the sperm should therefore give us information about effects confined almost entirely to the nucleus. Hinrichs ('26, '27) has observed loss of fertilizing power and other effects of radiations upon Arbacia sperm, but since the entire mercury arc spectrum of unknown intensity was employed, it is not possible to use her data for this comparison. The experiments outlined below were therefore performed to obtain the data required.
EXPERIMENTAL
The light from a quartz mercury arc was passed through a quartz monochromator and the desired wavelength selected with a slit. The intensity of the beam falling upon the quartz exposure cell was determined with a line thermopile. The apparatus was in general similar to that used in previous investigations (Giese, '38 b). The wavelengths isolated for further study were chiefly A' s 2654A and 28048, but some experiments were performed with A' s 3130 and 36608. Since the intensity of the radiation decreased with use of the arc, it varied from experiment to experiment. F o r h2654A it ranged from 7.46 to 12.28 ergs/sec./mm.2, for h 2804A from 5.81 to 9.11 ergs/sec./mm.2.