For lacZ staining: fix for 30 min-1 hour at room temp

For in situs: fix for 2 hours.

Bouin's fix stops the chromogenic substrates very effectively and also helps remove some of the trapped background stain. It stops the color reaction very effectively and much better than MEMFA which can result in the embryos turning black everywhere. Bouin's does stain the embryos yellow however. This yellow stain can be removed with multiple washes in buffered ethanol or PBS-Tween. Do not use Bouin's to fix before in situ. We did this once accidently and were unable to detect RNA at all.