This study examined whether chicken erythrocyte chromatin, whose great phys
icochemical stability is promoted by histone H5, has a critical electrolyte
concentration (CEC) value comparable to that of other chromatin types with
special condensed packing states but devoid of H5. The affinity for toluid
ine blue molecules under Mg2+ competitive binding action was thus investiga
ted. The CEC value was found to be 0.12 M, which is close to that of hetero
chromatin from mouse liver cells and to sperm chromatin with histone H1 var
iants. Acetic ethanol fixative was found to affect the CEC. possibly by inf
luencing the chromatin packing state and DNA phosphate availability through
dissociation of proteins from the DNA. The phenomenon of programmed cell d
eath was considered to contribute to high CEC values by inducing special st
ates of chromatin condensation.