We can now add that the proved existence of the antinucleons has very strongly corroborated this possibility, although we also know that the symmetry between electric charges breaks down for weak interactions. As far as astronomical means are concerned, a verification seems impossible in principle, because they depend on electromagnetic phenomena, which are invariant under charge conjugation. It is, however, interesting that the recent important discoveries about beta decay and the neutrino now give a method for looking for antimatter which, while still impossible in practice, is sound in principle, being based on weak interactions which are not invariant under charge conjugation. This method, if it could be executed, would solve unambiguously the question of the existence of antiworlds. If we observe a star and from its astronomical characteristics can decide that most of its energy comes from a known cycle, as for example the carbon cycle, which is domi-Although statistics on human mortality furnish one of the most extensive and reliable collections of biological data, general theories to account for the quantitative relationships between age and death rate have not been completely satisfactory. The essential observations which must be taken into account in any general theory of mortality are as follows:1) The death rate at any age (of The authors are members of the staffs of the Gerontology Branch, National Institutes of Health, Bethesda, Md., and the Baltimore City Hospitals, Baltimore, Md. nated by beta decays, we can see whether the antineutrinos coming from it are or are not of the same kind as the antineutrinos coming from a pile or from our sun by performing an inverse beta-decay experiment. If it should turn out that they are neutrinos •-different from those coming from the sun-then the star is of antimatter {14, 15).

The present communication offers evidence which suggests that the photosynthetic reactions are at least slightly reversible, inasmuch as plants which have been irradiated give off fight for a considerable period of time after illumination. It also seems likely that this reaction is quite distinct from fluorescence or simple phosphorescence in its behavior.The phenomenon here described was uncovered in an attempt to demonstrate the formation of energy-rich phosphorus during photosynthesis using the firefly luminescent system as an indicator of ATP formation (1). A mixture of chloroplasts and purified firefly extract gave appreciable light following illumination. However, the chloroplasts were found to be capable of doing this in the absence of the firefly extract, thereby ruling out, at the present, any conclusions as to phosphate intervention. Materials and MethodsThe light was measured with a 1P21 photomultiplier followed by two stages of amplification feeding into a Brown recorder. In order to give constant Brown recorder readings a circulating system was used. (See Fig. 1.) Chlorella, Scenedesmus, and Stickococcus were grown in Knop's solution at 20°C., aerated with 5 per cent CO2, and illuminated with fluorescent tubes. Characteristics of Chlorella LuminescenceThe simple experiment of starting the pump in the circulating system ( Fig. 1) at various times after the exciting light had been turned off was sufficient to show that fight was emitted at room temperature for as long as 30 seconds after illumination. Light production could be demonstrated for as long as 2 minutes after illumination when quanta were counted with the photomultipfier at liquid nitrogen temperatures. The decay curves shown in Fig. 2 were obtained by replacing the Brown with a Brush recorder (which has a fiat frequency response from D. C. to 100 cycles per second). In these curves the zero values have been set equal to 1 although in the 28°C. experiment much more fight was emitted (see Fig. 6). It will be seen that the temperature has a profound effect on the shape of the curve. A good fit is obtained for a bimolecular reaction at 6.5°C.

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