David M. Kydd

Fraccaro, Kaijser, and Lindsten: Child With 49 Chromosomes

crease in cells with 47 chromosomes (from 1 to 21 per cent). In addition the percentage of cells with structurally abnormal chromosomes rose from 1 to 22. Three days later the unusually low count of modal cells was stili present and on this day the percentage of cells with chromosome structural abnormalities reached a maxImum. By the fifth day the percentage of modal cells had returned to the pretreatment limit and so remained. Although the percentage of cells with structural abnormalities of the chromosomes had declined by the fifth day, 9 to 10 per cent of the cells were still abnormal on the ninth and tenth days. In both patients unusual numbers of polypoid cells were seen after therapy. Although much more work will be necessary to understand the pattern of the changes, particularly the effect of varying the total dose and dose rate, x-rays readily produce chromosome damage which can he detected in cultures of human blood cells. David M. Kydd