[Histonet] cloudy cornea after Hartman's fix

[John Kiernan]

The cornea consists of cells (nuclei with plenty of cytoplasmic protein) and parallel bundles (lamellae) of collagen fibres, also protein. It is wonderful that the normal cornea is transparent.

Doesn't any fixative make the cornea opaque?
Davidson's (=Hartmann's) fixative contains plenty of formaldehyde (to add to and slowly crosslink all protein molecules, including collagen fibrils) but perhaps not quite enough ethanol to rapidly coagulate soluble proteins in cytoplasm.
(Davidson's 22.2% v/v EtOH is slightly more than in sherry, madeira or vermouth; about half of that in whisky, gin etc.)  The acetic acid (about 10%) can be expected to make nuclear DNA molecules and their associated proteins shrink into the patterns we see as typical of different cell-types.

Most of the many formalin-acetic-alcohol fixatives contain enough ethanol to bring about protein coagulation before the more slowly reacting formaldehyde does its stuff. As Tony points out, more research is needed.

John Kiernan
https://www.schulich.uwo.ca/anatomy//people/faculty/emeriti/kiernan_john.html
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From: Tony Henwood via Histonet <histonet at lists.utsouthwestern.edu>
Sent: June 27, 2024 7:17 PM
To: histonet at lists.utsouthwestern.edu <histonet at lists.utsouthwestern.edu>; Davoli, Katherine A <katherine.davoli at pitt.edu>
Subject: Re: [Histonet] cloudy cornea after Hartman's fix

Hartman's (also known as Davidson's) fixative is sometimes used to reveal lymph nodes in resections where they appear opaque - white. It is not surprising that the tissues of the eye would react the same.
I assume that the alcohol causes the bleaching of the tissue (or is it the acetic acid?) - more research needed.

Regards,

Tony Henwood MSc, BAppSc, GradDipSysAnalys, CT(ASC), FFSc(RCPA) (Retired)
Principal Scientist, the Children’s Hospital at Westmead (Retired)
Adjunct Fellow, School of Medicine, University of Western Sydney.
________________________________
From: Davoli, Katherine A via Histonet <histonet at lists.utsouthwestern.edu>
Sent: 28 June 2024 04:12
To: histonet at lists.utsouthwestern.edu <histonet at lists.utsouthwestern.edu>
Subject: [Histonet] cloudy cornea after Hartman's fix

Anyone know why the cornea of my pig eye got white/cloudy on dropping it in to Hartman's fixative?  I'm used to working with mice where, if this happens I didn't notice.

Katherine Davoli, MDiv, HTL(ASCP)cm    (they/them/theirs)
Lab Manager, Tissue Culture & Histology Cores, U. Pitt Dept of Ophthalmology
7.373 UPMC Mercy Pavilion        1622 Locust St., Pittsburgh PA 15219
(412) 624-8508   this number cannot receive texts
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