[Intensity of the Feulgen reaction depending on the method and duration of fixation]

A comparative cytophotometric investigation of DNA-fuchsine content in mature erythrocytes of chicks was carried out using various methods and duration of fixation: 96 degrees and 100% ethanol, Carnoy's fixative, and mixtures of 40% formalin--96% ethanol--glacial acetic acid /GAA/(9 : 3 : 1), 100% methanol--4% formalin--GAA (17 : 2 : 1), and 96% ethanol--GAA (3 : 1)+formalin (final concentration 2%). The duration of fixation varied from 15 to 150 minutes, with 15 minutes intervals. It has been shown that the quantity of DNA--fuchsine (under equal conditions of the Feulgen reaction) depends greatly on the method and duration of fixation. Of the fixatives investigated the best is the mixture of 96% ethanol--GAA (3 : 1)+formalin 2%, after which the Feulgen reaction runs more intensively, and practically does not depend on the fixation duration. The structure of chromatin (determined by the distribution character of optical densities in each point scanned) is also best preserved. The Carnoy fixative occupies, by these parameters, the last place. The mechanisms of interaction of the above fixative with the nuclear DNP are discussed briefly.