[Histonet] Freezing tissues

[Martin S.]

Hi there,
 
I need to freeze some mouse spleens tomorrow for cryosectioning. Usually
I cut the spleen in half and place it in OCT in a foil mould. I then
place the foil mold in a petri dish of isopentane sitting on dry ice.
This seems to work well and I dont have problems with ice crystals or
freezing artifacts. However, after the holidays there is not a drop of
dry ice to be found in our institute so I need some advice on another
method - possibly using liquid nitrogen. I've read a number of methods
whereby you immerse the tissue directly in the LN, hold the tissue in
the LN vapours or do as I do with isopentane but have the petri dish
floating on LN (is this possible?).
Any suggestions greatly appreciated!
 
Thanks
Sonya