Hello Tony,

I've not seen this one specifically, but it looks like
one of the "home made protargol" publications of the
1940s and 1950s. For example: Davenport HA, Porter RW, 
Myhre BA (1952) Preparation and testing of silver-protein 
compounds. Stain Technology 27: 243-248. In this paper,
the "best" silver protein was made from silver nitrate
and peptone. [For what it's worth, I tried their method
many years ago and couldn't get it to work.]
  The expected effects of adding gelatin or other protein
to a dilute silver nitrate solution are (1) to lower the
concentration of sliver ions, by complexation, and
(2) possibly to retard the action of the developer - the
quick dip in water at Step 3 is probably a critical
one, allowing a small amount of the silver solution to
be carried over into the sulphite-hydroquinone.
  Gelatin was used in one of GJ Romanes' earlier silver 
methods for axons (J Anat 80:205-206, 1946). This was
in an ammoniacal solution containing tannic acid; it's not 
the same as his better known 1950 method, which uses a
silver solution with a more studied composition, without
any "natural" ingredients (J Anat 84:104-115).
--
John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London,   Canada   N6A 5C1
   kiernan@uwo.ca
   http://publish.uwo.ca/~jkiernan/
----------------------------------------
> Tony Henwood wrote:
> GELATINE SILVER FOR NERVE FIBRES
> Principle:
> Nerve fibres and axons have the ability to absorb silver ions
> that are then reduced by hydroquinone.  The fibres are further
> darkened by oxalic acid.  Selectivity is improved by including
> gelatine in the silver solution.
> 
> Fixation:      10% buffered formalin.
> Microtomy:     Paraffin sections at 5um.
> 
> Reagents:
> 
> 1.      Impregnating solution - prepare just prior to use:
>         Distilled water                                 50ml
>         Silver Nitrate                                  0.1g
>         Gelatine                                        0.4g
>         Place at 60oC for 15 minutes, mixing twice.
> 
> 2.      Reducing solution:
>         Distilled water                                 50ml
>         Sodium Sulphite                                 0.5g
>         Hydroquinone                                    0.1g
>         Mix, stand for 20 minutes before use.
> 
> 3.      0.2% Gold Chloride
> 
> 4.      2% Oxalic acid
> 
> 5.      2% Sodium Thiosulphate.
> #012#Procedure:
> 
> 1.      Dewax and hydrate sections to distilled water.
> 2.      Place in impregnating solution, 5 hours - overnight
> (60oC).
> 3.      Dip slide in distilled water once.
> 4.      Place in reducing solution, 2 hours.
> 5.      Running water, 10 minutes.
> 6.      Distilled water, 1 minute.
> 7.      Gold Chloride, 5 minutes.
> 8.      Distilled water, 1 minute.
> 9.      2% Oxalic Acid, 2 minutes or longer.
> 10.     Running water.
> 11.     2% Sodium Thiosulphate, 5 minutes.
> 12.     Wash in water, 5 minutes.
> 13.     Dehydrate, clear and mount.
> 
> Results:
> Axons and nerve fibres          black
> Nuclei                          shades of grey
-- 
-------------------------