Mast cells in tissue from different species do not all behave the 
same.  Nor do mast cells at various stages of their own metabolic 
functions.  This is especially true if you are using metachromatic 
methods to demonstrate them.

For Really good demonstration, try alcian blue pH1.0 on frozen 
 unfixed sections, but do not be surprised if the edges of the cells 
are a bit fuzzy - unfixed sometimes means "unlocalised" as well.
Russ Allison, Wales