Some of them bind specific sites like mitochondria in the cytoplasm in vivo , hence vital stain. They are normally used in very dilute concentrations to avoid any interference between the living state and the stain itself. Ultimately, each vital stain may lead to cell deterioration especially in higher concentration. A wonderful account about vital stains written by Richard L. Howey can be found in the Micscape Library. The vital stains entering into the cell or tissue cause visible changes.
Some fixatives cause a rapid and sometimes excessive loss of such structural components.
Consequently, fixed cells or tissues undergo irreversible changes during fixation. If you apply a method of chemical fixation and your fixative contains alcohol, you have to expect visible deformities due to severe shrinkage caused by cell dehydration. Nevertheless, many still prove to be very useful and even unique in some specific conditions. Unfortunately osmic acid and some other fixatives are extremely toxic and should only be accessible and safely used in professional laboratories. For chemical fixation there must be a compromise.