Another fixative in this general group that deserves honourable
  mention is the "Modified Carnoy" described in James & Tas (1984)
  Histochemical Protein Staining Methods. R.M.S. Handbook 4. Oxford.
  This is Carnoy with only 5 ml of acetic acid (making 5/95*100=5.26%).
    Perhaps there's an earlier description of this fixative, by someone
    with an unpronounceable 5-syllable Russian name. I haven't checked
    exhaustively and don't intend to. 

  With the lower acetic acid concentration there is less extraction
  of RNA. Cytoplasmic staining by basic dyes (Nissl stains etc) is
  brighter than after regular Carnoy, and you don't lose all the 
  stainable RNA if you leave specimens in it for too long. (I
  had this happen once with some mouse brains left for about 36
  hours in Carnoy. All Nissl substance gone for ever. This was well
  before 1984!) Otherwise, modified Carnoy is the same as the original: 
  microanatomical preservation better than after neutral formalin but 
  not as good as after Clarke's, Zenker's or SUSA. Modified Carnoy is
  the only recommended fixative for selective RNA staining with
  cuprolinic blue, but I don't think it has been compared with any
  fixatives other than formaldehyde for use with this method.

                                                   John Kiernan
                                                   London, Canada.
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On Wed, 26 Apr 2000, Gayle Callis wrote:
> Clarkes fixative is SIMILAR to (NOT the same!) as Carnoys without the
> addition of chloroform
>   Clarkes  results in 25% acetic acid 
>    25 ml acetic acid
>    75 ml 100% ethanol
> Carnoys without the 30 ml of chloroform results in 16.67% acetic acid, 
>    10 mls acetic acid
>    60 mls 100% ethanol
> There is another fixative that is 5% acetic acid in 95% ethanol, called
> Meiers fixative ... wonderful immunofluorescent IgG, IgA, and IgM staining
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