Human chromosomes may be readily studied by in vitro culture of leukocytes obtained from peripheral blood1 (or even from bone marrow) to which phytohemagglutinin2 has been added. The dividing cells are lymphocytes and perhaps monocytes,3,4 and their chromosomal complement is representative of that of other body cells.4 Cells of skin and fetal and other tissues, including neoplasms, can be grown in tissue culture and studied in mitotic metaphase, but these preparations are not as readily suitable for study of chromosomes. Tjio and Levan5 in 1956 greatly stimulated interest in chromosomes by their presentation of the human karyotype.
The purpose of this study is to explore the effects of in vivo x-radiation on the chromosomes of normal human somatic cells. This has been done by analyzing cultured leukocytes from cancer patients who have had much hemopoietic tissue exposed in the course of x-ray therapy. Taking samples