The experiments showed that a prolonged exposure of six months to a temperature of about -190° has no appreciable effect on the vitality of micro-organisms. To judge by the results there appeared no reason to doubt that the experiment might have been successfully prolonged for a still longer period.
[27] White, J., _Proc. Roy. Soc._, 1909, B, lxxxi., 417.
[28] Macfadyen, A., _Proc. Roy. Soc._, 1903, lxxi., 76.
Paul Becquerel[29] found that seeds which possess a very thick integument may live longer than the grain in Miss White's experiments. The thickness of the integument prevents the exchange of gases between air and seed. Thus seeds of leguminoses (_Cassia bicapsularis_, _Cytisus biflorus_, _Leucæna leucocephala_, and _Trifolium arvense_) had retained their power of germination for eighty-seven years. Becquerel has shown that the dryness of the membrane is very essential for such a duration of life, since when dry it is impermeable for gases and the slow chemical reactions inside the grain become impossible.
[29] Becquerel, P., _Revue générale des Sciences_, 1914, xxv., 559.
In the cosmic space there is no water vapour, no atmosphere, and a low temperature, and there is hence no reason why spores should lose appreciably more of their germinating power in ten thousand years than in six months. We must therefore admit the possibility that spores may move for an almost infinite length of time through cosmic space and yet be ready for germination when they fall upon a planet in which all the conditions for germination and development exist, _e. g._, water, proper temperature, and the right nutritive substances dissolved in the water (inclusive of free oxygen).
While thus everything is favourable to Arrhenius's hypothesis, Becquerel raises the objection that the spores going through space would yet be destroyed by ultraviolet light. This danger would probably exist only as long as the germ is not too far from a sun. The difficulty is a real one since the ultraviolet rays have a destructive effect even in the absence of oxygen. It is possible, however, that there are spores which can resist this effect of ultraviolet light. Arrhenius's theory can not of course be disproved and we must agree with him that it is consistent not only with the theories of cosmogony but also with the seeming potential immortality of certain or of all cells.