Sex, Sex Inheritance and Sex Determination in Paramecium Aurelia.

those produced by x-irradiation, the above result and further experiments producing mutations with neutrons may lead to new conclusions regarding the interaction of radiation ions with genes and hence of the size and structure of the gene. It is interesting to note that the ratio of effectiveness (5 or 6 to 1) for the effects on mature sperm of neutron as compared with x-irradiation is comparable to that for carcinoma cells (5 or 6 to 1), and actively sprouting seedlings (5 to 1), but greater than that for Drosophila eggs (2.1 to 1), for fern spores (2.5 to 1) and normal mice (4 to 1), all of which were dosed by the same method. The action on mature sperm measured in the experiments here described is one in which chromosome changes probably are much the most important element. It may be possible by further study of ratios of effectiveness to determine the cell element which first breaks down under irradiation in any given case. Results obtained in later generations will be reported in a subsequent paper. We appreciate the interest and cooperation of both Professor Ernest 0. Lawrence and Dr. John H. Lawrence. One of us (P. C. A.) participated in this work as a Fellow in Radiation Studies supported by the Christine Breon Fund of the University of California Medical School. This investigation has been aided by grants from the Josiah Macy, Jr., Foundation and the Committee on Radiation of the National Research Council. 1-Lawrence, J. H., and Lawrence, E. O., Proc. Nat. Acad. Sci., 22, 124-133 (1936). 2 Lawrence, J. H., Aebersold, P. C., and Lawrence, E. O., Ibid., 22, 543-557 (1936). 3 Zirkle, R. E., and Aebersold, P. C., Ibid., 22, 134-138 (1936). 4Zirkle, R. E., Aebersold, P. C., and Dempster, E. R., Am. Jour. Cancer, 29, 556-562 (1937). 5 Whiting, P. W., Science, 84, 68 (1936). 6 Snell, G. D., Jour. Exptl. Zool., 65, 421-441 (1933).