16. Nasjleti, C. E., and Spencer, H. H. Chromosome damage and poliploidization induced in human peripheral leukocytes in vivo and in vitro with nitrogen mustard, 6-Mercaptopurine and A-649. Cancer Res. 26(1): 2437-2443, 1966. 17. Nichols, W. W. The role of viruses in the etiology of chromosomal abnormalities. Am. J. Hum. Genet. 18(1): 81-92, 1966. 148