Time in zinc fixatives
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.
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