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MARCUS W. H. BISHOP

Summary.

This essay advances the theory that an unsuspectedly large part of embryonic death is attributable to genetic causes. The genetic factors involved are not necessarily inherited by the parents, indeed the majority probably arise de novo in each parent generation and some are likely to arise in the definitive gametes. The theory seeks to account for the nature of unexplained fertility differences between males, and of idiogenic infertility, and of some of the decline in fertility that is associated with age. It suggests that a considerable part of embryonic death is unavoidable and should be regarded as a normal way of eliminating unfit genotypes in each generation.

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W. R. LYSTER and MARCUS W. H. BISHOP

Summary.

Seasonal variations in secondary sex ratio in man in Perth, Adelaide and Brisbane appear to be influenced by seasonal variations in rainfall. In these cities, the onset of the rainy season is followed about 11 months later by a larger than normal excess of male births. Sex ratio in Sydney, however, where rainfall is more evenly distributed throughout the year, does not vary markedly with season; but a relationship between rainfall and sex ratio again becomes apparent when the data are analysed in terms of wet months and dry months and of wet years and dry years. It is suggested that secondary sex ratio is affected by properties of drinking water that alter with variations in rainfall, and that the property of water concerned is probably its content of trace elements. Support for this hypothesis has been obtained from an examination of sex ratios in two regions of Australia with trace-element deficiencies. It is also suggested that drinking water exerts its effect through the male parent and that the observed variations in secondary sex ratio reflect similar variations in primary sex ratio.

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MARCUS W. H. BISHOP and JOHN SMILES

Summary.

A simple method is described for differentiating the acrosome in living mammalian spermatozoa and spermatids by induced fluorescence with acridine orange. Observations were made on spermatozoa from man, the bull, the rabbit, the hedgehog, the greater bush-baby, the greater horseshoe bat and eight species of rodent, and on spermatids from five species of rodent. With the exception of human spermatozoa, nuclei fluoresced bright apple green and acrosomes fluoresced bright red where they extend beyond the nucleus, and yellow or yellow-green where they overlap the nucleus. Human spermatozoa fluoresced entirely green, yellow-green or red and actively motile spermatozoa of each colour were seen simultaneously. The significance of the results and some problems associated with the method are discussed.