Can someone explain the mechanism involved with having specimens free-floating in PBS and why that is not desirable if you will be freezing the specimen later?  I've always known that saline or PBS dampened gauze is best for muscle biopsies for subsequent frozen section, but I've never known why.

I am dealing with horrible freezing artifact with some specimens today (testes), and the only difference between those and previous ones were the amount of time spent free-floating in PBS.

Also, is there any reason NOT to cryopreserve fresh, unfixed specimens for frozen embedding?

Thanks, as always,

Teri Johnson
Managing Director Histology Core Facility
Stowers Institute for Medical Research
1000 E. 50th St.
Kansas City, Missouri  64110
tjj@stowers-institute.org