The tissue should be put into the fixing fluid as soon as possible after its removal from the body. It must not be allowed to dry. There should be an abundance of the fixing solution, 25-50 times the volume of the object to be fixed. The tissue should never be put into a dry vessel and the fixing fluid poured upon it; the vessel should first be filled with the fixing solution and the tissue then dropped into the latter. A slight agitation of the fluid will prevent the sticking of the tissue to the bottom or sides of the vessel. The size of the pieces must be adapted to the penetrating power of the fixing reagent, but as a rule the pieces should not be more than 2-3 cms. in thickness, and for some reagents 0.5 cm. is as thick as they can safely be. The reagents used should be changed when they become cloudy or discolored. The used solution may be filtered and used again, but some reagents can be used but once. Alcohol may be saved for redistillation. In the case of some reagents (mercuric chloride, chromic acid, osmic acid, etc.), the time limits of the fixation should not be exceeded, as over-fixation will ruin the staining-power of the tissues. Alcohol is practically the only solution in which tissues may be left indefinitely, but even with it there are certain limitations. As a general rule the time required for fixation may be shortened by keeping the reagents at incubator-temperature. As the different fixing reagents vary so greatly as to their especial advantages and disadvantages these will be considered separately. Only the best and most commonly used methods are here included.