ABSTRACT
Pre-treatment for the study of chromosomes is generally performed for several special reasons. It may be carried out for: clearing the cytoplasm, separation of the middle lamella causing softening of the tissue, or bringing about scattering of chromosomes with clarification of constriction regions. Although osmium fixation preserves chromosomes during the divisional cycle, it cannot be recommended for the study of the interkinetic nuclei. Materials, after osmium fixation, require bleaching to remove the black precipitate produced by fats, usually, with hydrogen peroxide when the slide is brought down to water prior to staining. Of all the different staining methods employed for the study of chromosomes, the Feulgen reaction is considered to be the most effective with regard to chromosome staining. At least for the study of chemical effects on chromosomes, orcein staining should preferably not be applied as its effect may often mask the effect of chemicals.
