Under controlled conditions, ammoniacal silver (A-S) stains the bands of Dipteran salivary gland chromosomes in a precise and selective manner. Such staining is dependent upon the histone content of the band, as shown by the effects of selective extraction and blocking of the histones. The effects of qcid extraction and HONO solution on the A-S staining of different bands suggest that specific genes may have particular histones associated with them.

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A B S T R A C TAn acute effect of antigens on the nuclear histones of mouse thymocytes was investigated by means of cytophotometric measurements of thymocytes stained with ammoniacal-silver (A-S) and with fast green (FG). In addition, the D N A content was measured in terms of Feulgen staining. In terms of such staining it appeared that nuclei of control thymocytes contain a greater amount of nuclear histones and a higher histone/DNA ratio than do renal cell nuclei from the same animal. Within l hour after the injection of antigen the thymocyte nuclei appear to lose approximately 32 per cent and 20 per cent, respectively, of A-S and FG stainable nuclear proteins, while the Feulgen staining remains unchanged. Since the renal cell nuclei show no antigen-induced change in histone staining, the histone staining and histone/DNA ratios were found to be similar in the thymocytes and renal cells of the antigen-injected mice. The antigen-induced loss of thymocyte histones was also found to be associated with a change in the color of the A-S staining, from yellowish brown to black. This and other findings suggest that thymocyte nuclei contain an antigen-labile, lysine-rich histone. The implication of these observations in regard to the phenomenon of immunological competence is discussed and the need for continued investigation indicated.

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