B-5 fixative - heating to prepare


Mary Ann Deathridge at Vanderbilt asks:

>>We have a procedure for making B5 fixative that calls for heating the water 
to 90 C. Could anyone tell me the reason why? Would overheating cause the 
mercury to precipitate? Our docs are set on using B5. Does anyone know where 
to commercially purchase this fixative?<<

Mercuric chloride is about twice as soluble in hot water as it is in cold 
water, and dissolves a lot faster - so I usually use hot tap water to 
dissolve it when I prepare B-5 fixative. Some may precipitate out on cooling, 
but the published formula should result in a saturated solution at room 

This doc is definitely set on B-5 for lymphomas, though aware of the 
problems. Pathologists should be strongly encouraged to use as small amounts 
of it as possible - no more than 10 mL per case - and to cut tissue very thin 
before fixation. 

B-5 has been available from Poly Scientific - may still be. You have to add 
the formaldehyde before using it, of course.

Bob Richmond
Samurai Pathologist
Knoxville TN

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