Abstract
Summary
Treatment with ammonia reduces the sensitivity of chromosomes to X-rays. Curves showing the decrease in sensitivity as a function of ammonia concentration are presented. The results are taken as evidence in support of the hypothesis, previously advanced, that the sensitivity of chromosomes to X-rays at the onset of prophase may be attributed to the presence of positive charges on the separating surfaces of the dividing chromonema. These separating surfaces are probably made up of proteins of the histone type.
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