Gayle Callis asked about times and volumes needed for good fixation 
when using zinc fixatives.  The times I gave were for properly 
grossed tissues no more than 5 mm thick.  Whole organs or large 
chunks will take much longer, as the penetration rate is the same as 
for NBF:  about 0.5 mm/hr through easily penetrated tissue like 
liver.  Zinc formalin is faster than NBF, not because it penetrates 
faster but because it reacts faster once it gets in.

Our feeling is that if you want gross museum specimens, leave the 
stuff in fixative for weeks, but if you want fine histological 
specimens, you must cut these organs up thinly or autolysis will take 
over before the fixative can work.  conventional breadloafing 
techniques are really too crude for good quality histology, again 
because the slices of "bread" are just too thick.

As for volume, a minimum of 20 to 1 is essential.  Changing the 
solution will aid fixation rate, most especially if the volume is 
less than ideal.  However, frequent changes will not get around the 
problem of autolysis in large specimens.

Dick

-- 
Dick Dapson
Anatech Ltd.
1020 Harts Lake Road
Battle Creek, MI  49015
800-ANATECH (800-262-8324)
email@anatechl