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than did either the control of X-irradiated cells. Phospholipid levels were equal for all groups of cells. Thus the effects of 2
H 2
O on lipid synthesis are qualitatively quite similar to those of radiation damade. An interisting observation that deserves further scrutiny relates to the radiation sensitivity of deuterated cells. Usually, cells grown and irradiated in
2 H 2
O shown much less sensivity to radiation than ordinary cells suspended in water. Suspension of ordinary cells in 2 H 2
O did not have any effect on the reduced sensitivety became apparent.
A serious alteration in cell chemistry must be reflected in the ability of the cells to divide in the presence of 2 H 2
O and in the manner of its division. However, a many statements suggesting that 2 H 2
O has a specific action on cell division are common since today. Probably it may be true that rapidly proliferating cells are highly sensitive to 2
H 2 O, but that deuterium acts only to prevent cell division is unlikely.
The rabbit cells grown on medium containing the various concentrations of 2 H 2 O shown
, that 2 H 2
O caused a reduction in cell division rate, and this effect increased as the concentration of 2 H 2
O or duration of exposure, or both, were increased ( Lavillaureix et all., 1962) . With increasing concentration of
2 H 2 O the frequency of early metaphases increased, accompanied by proportional decreases in the other phases.
It was suggested that 2 H 2
O blocks mitosis in the prophase and the early metaphase of many cells grown in 2 H 2
O. The blockage, however, was overcome if the initial concentration of 2 H 2
O was not too high and the exposure time not too long. In

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