ZINC AXD IBON 19 



the sole method that has been developed. Zinc is precipitated by 

 nitropmsside and the precipitate is brought out as a deep purple 

 by treatment with sulfide. 



Mendel and Bradley Alethod for Zinc 



SPECI.\L REAGENTS 



10% Sodium Xitroprusside. 



Potassium Sulfide Solution. (Concentration not stated, but 1-5% 

 should suffice.) 



PROCEDLTIE 



1. Prepare paraffin sections. (!Mode of fixing tissue not given, 

 but, as in all other cases, the freezing-drying treatment, see page 3, 

 would be preferable.) 



2. Treat sections with the nitropmsside soln. for 15 min. at 50^. 



3. Cool, and wash in a stream of water for about 15 min. 



4. Introduce under cover glass placed on section 1 drop of the 

 sulfide soln. 



Result. Zinc elicits an intense purple color. 



IRON 



The classical histochemical tests for iron are the Prussian and 

 Turnbtiirs blue reactions and the hematoxylin method of Macallum. 

 the latter being the least specific (Lee's Vade Mecum, pages 2S9- 

 292). The Prussian blue test will detect ferric, and Turnbull's blue 

 ferrous, iron. More recently other methods have been proposed for 

 which certain advantages have been claimed. The dinitrosore- 

 sorcinol test of Humphrey (1935) brings out iron as a rich green 

 of pristine brilliance and the color is much more permanent than 

 that of Prussian or Tiu-nbull's blue, which fades after a year or two. 

 Thomas and Lavollay (1935) employed the 8-hydroxj-quinoline 

 reaction to ^-isualize iron in greenish-black; other metals appearing 

 in various shades of green and yellow. The strong flourescences of 

 metallic 8-hydrox^-quinolinates may also be used for identifications 

 (see page 108). 



Iron, like many other metals, occurs in tissues both in the in- 

 organic or free form, and in the organic or bound form. Before 

 bound iron can be visualized it must be converted to the free form. 



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