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It is essential not to cram too many pieces of tissue into one pot.  For example in this first case there are too many large pieces of tissue to be adequately fixed . It can be seen that the centre of the specimen remains unfixed  (the edge is brown [fixed], whilst the centre is pink [unfixed]) and will give a poor histological result. If several pieces need to be sent they should be of appropriate size. .  In this second example a splenic mass (approx. 4cm diameter) was placed in a pot of a similar diameter to the size of the mass .  and remained unfixed 24 hours later.  A sample of this size needs to be placed in a much larger pot. 

Some organs, for example the eyes and brain require special mention. The eyes should be removed whole, preferably cleaned of some of the muscle and fat, and with as much optic nerve as possible left intact, placed into an adequate amount of NBF. Dog or cat eyes can be placed in 100ml pots 100ml pot containing 50-60ml of fixative. They can then be prepared for processing at the laboratory.