“…Feulgen photometry is now extensively used to estimate relative amounts of DNA in individual nuclei (Leutcheriberger, 1954;Swift, 1955;Vendrely and Vendrely, 1956;Waker, 1959;McLeish, 1961). The validity of this method has been well established by comparisons between estimations of Feulgen stain values with chemically determined estimates of DNA in the same material (Deeley, Davies and Chayen, 1957;Ris and Mirsky, 1949;Leuchtenberger, 1954;McLeish and Sunderland, 1961).…”