[Histonet] Histonet Digest, Vol 243, Issue 7

[Bob Richmond]

>
> Re: [Histonet] Modified Davidson
>
> The formula for "modified Davidson's fixative" that I used was three parts
tap water, three parts reagent alcohol, two parts 37% formaldehyde ("strong
formalin"), one part glacial acetic acid. Best mixed under a fume hood.

At 85 I must be one of the last left standing with much experience with it.
I learned it when I was a resident at Johns Hopkins around 1970, when
surgical pathologist Bill Hartmann introduced it at the request of medical
geneticist Victor McCusick, who wanted it for fixing skin biopsy specimens
to look for nuclear sex chromatin bodies ("Barr bodies") as specified by
Moore & Barr in their 1950s publications on this important discovery.

The fixative got quite popular with the GYN pathologists, who ran an
entirely separate service, replacing their old "Vandegrift's fixative" for
all their specimens. From there it seems to have spread to other pathology
services, eventually becoming various proprietary fixatives such as "O-Fix".

You could always identify it by the characteristic "airplane dope" (for
boys)" or "nail polish remover" (for girls) aroma, as ethyl acetate
accumulated in the aging fixative as the alcohol and acetic acid slowly
esterified. The "modified" referred to the omission of glycerol from what
was supposed to be Davidson's original formula.

John Kiernan some years ago noted on Histonet that the formula wasn't
entirely rational, and was very tolerant of various modifications. He said
then that when he retired he'd try to find Davidson's original source among
Davidson's unpublished papers.

I think Davidson's fixative became largely obsolete for two reasons. Better
embedding waxes gave much improved nuclear detail over plain old paraffin
wax (what I remember long ago). And it isn't compatible with
immunohistochemical techniques.

Bob Richmond
Maryville, Tennessee