It is possible to put frozen tissue in NBF and get good results by H&E. I
once had a bull dog submitted for necropsy that had suffocated at a
groomer's shop. The owner was sure it had been strangled and submitted it
as a legal case. He put the dog in a deep freeze with dry ice and it came
in frozen sollid. I figured histo would be terrible but I had to do it
anyway. Of course, it was a Friday. I left the dog to thaw on the table
all day but by the end of the day it was still very crunchy. I figured it
could not be any worse frozen than thawed so I finished the exam. I put
the tissues in NBF still crunchy. I fully expected severe freeze
artifact. In fact, there was NONE. Since then I have occassionally
received bottles of NBF fixed tissues in the mail in the winter that had
been frozen in NBF. These were terrrible. They had severe fracturing
histologically. In these cases, I have taken some of the unfixed tissue
submitted for virology that was also frozen and put in in NBF. These were
fine. 

Douglas Gregg DVM, PhD
Veterinary pathologist
Plum Island animal Disease Center
Greenport, NY 11971