Abstract
LONDON Royal Society, June 21. P. D. F. MURRAY: Uncoordinated contractions caused by tsgg-white and by alterations in the cation ratio of the medium, in the heart of the chick embryo in vitro. If suitable fragments of chick embryos in primitive streak stages be explanted into the egg-white of four- or five-day eggs there occurs a differentiation of contracting cardiac tissue. The contractions differ from those seen in similar explants in plasma in lacking coordination, each cell contracting independently of the others. When entire hearts of 2-day embryos are similarly explanted into egg-white, the co-ordinate beat always stops, and is usually replaced by uncoordinated contractions. This anarchic activity is given the provisional name of ‘twitter’. It is caused by the high potassium content, aided by the lower, but still rather high calcium content, and by the low content of sodium. K. MELLANBY: The site of loss of water from insects. An apparatus is described which will measure the amount of water evaporated from an insect, and is accurate to a hundredth of a milligram. The rate of loss of water from three species of insects was determined; (1) in dry air, (2) in air to which 5 per cent of carbon dioxide had been added, and (3) in a mixture containing less than 1 per cent of oxygen. In insects with a spiracle-closing mechanism the rate of loan of water under (1) and (2) (which caused them to keep their spiracles open permanently) was 2-7 times that in dry air. In insects which could not close their spiracles, the rate of loss of water was practically the same under all conditions. 2 per cent carbon dioxide is sufficient to cause insects to keep their spiracles permanently open; oxygen has to be reduced below 1 per cent to have the same effect. From these experiments it appears that practically all tho water evaporated is lost by way of the trachcal system, and that a thin integument may be just as watertight as one which is highly 'sclerotised'. P. A. BUXTON and D. J. LEWIS: Climate and tsetse flies: laboratory studies upon Glossina submorsitans and tachinoides. It is already known that the number of tsetse flies which can be captured under standard conditions rises and falls with the season, and that many of the species are sharply limited to particular types of vegetation. It is thought that the limits are climatic. Observations made under controlled conditions in the laboratory support those made in the field; taken together, the results should tend to give precision to the control of Qlossina, which will probably be achieved by altering the vegetation and with it the micro-climate.
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Societies and Academies. Nature 133, 994–996 (1934). https://doi.org/10.1038/133994a0
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DOI: https://doi.org/10.1038/133994a0