There are some articles on this matter:
= Formaldehyde (Formalin) fixation at lower temperature (4°C) better preserves Nucleic acid integrity (2011), cf.
( http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0021043)
= Formaldehyde (Formalin) at higher temperature (37°C vs. 4°C) preserves glycogen far better, cf.
The effect of fixatives and temperature on the quality of glycogen demonstration
Yosef Mohamed Azzam Zakout , Magdi M Salih, HG Ahmed, Biotechnic & Histochemistry 2010, 85(2): 93–98
and, in this reply as last citation for thinking over and for all those not knowing the important basic scientific articles written by their scientific predecessors: e.g.,
= Formaldehyde Fixation
by CECIL H. FOX, FRANK B. JOHNSON, JOHN WHITING, and PETER P. ROLLER
Review Article
The Journal of Histochemistry and Cytochemistry Vol. 33, No. 8, pp. 845-853, 1985
Copyright © 1985 by The Histochemical Society, Inc. Printed in U.S.A.
cf: p.847,left row,second last and last paragraph:
<<An oversight, first by Blum, but perpetuated by countless others, is the question of temperature for fixation. Some investigators reasoned that since unfixed tissues undergo autolysis and since formaldehyde is known to fix slowly, one should retard autolysis by chilling the tissues and fixative. Other investigators assume that fixation is not a chemical reaction in the usual sense and fix tissues at room temperature. The choice of temperature has probably also been affected by the problems that were assumed to occur if formaldehyde was heated much above room temperature. Certainly the easiest alternative to the question of the ideal temperature for fixation is to use that most readily accessible—ambient temperature.
The temperature problem is also linked to the problem of length of fixation. Classical sources recommended that tissues be fixed for at least 24 hours (21). The advent of automatic tissue processing machines has taken a serious toll on the quality of fixation; a situation that is compounded in hospital practice by efforts to produce a diagnosis as quickly as possible with the intention of reducing the costs of medical care by decreasing hospital stay. The result is that in many diagnostic situations tissues are exposed to 1.3 M formaldehyde at room temperature for only a few hours, or occasionally, a few minutes.>> end of citation, cf. http://decapoda.nhm.org/pdfs/1505/1505.pdf
Souce: NovoPro 2018-03-13