The optimal tissue size is no thicker than 1-2mm. The Volume of fixative should be at least 10x the volume of the tissue. However, excellent results have been obtained with Carnoy's, B5, and formaldehyde. Zenker's and Telly's fixatives have seldom provided satisfactory results. Place in 10 volumes of fixative.
Cold fixative is better than warm or room temperature fixative.
After one hour, inspect sample. If the fixative is cloudy, replace with fresh fixative. If the sample is thick, remove sample, place on a cutting board, cut 1-2mm slices to expose all surfaces and return to 10 volumes of fixative. BUT no longer. In the case of the mammary gland, the gland should be spread on a slide so that the fat does not inhibit fixation.