If large specimens are not fixed well internally, distortion or collapse may result during subsequent procedures. Some tissues ie brain, lung, vascular tissue, kidney must be perfused for acceptible results. Lung requires double - airway and vascular. Whole body vs site perfusion. Temperature Procedures involving osmium and permanganate are often carried out in an ice bath.- easier to control the rate of fixation and slows down autolytic processes.
Some individuals prefer to carry out all fixation in ice bath.
If enzyme cytochemistry is to be carried out, fixation is virtually always at ice bath temp. Duration Underfixation should be avoided. Excessive time in a fixative can cause leaching of some components, such as calcium and glycogen. Cell size and shape remains constant. Hypertonicity - solute concentration of fixative is greater than cytoplasm.