CHAPTER XXVI. 299 



ORGANIC IRON COMPOUNDS. These will not give the iron 

 reactions unless the complex iron compound has been broken up, 

 that is, the iron " unmasked " by some reagent : acid alcohol is 

 used for this. Sulphuric acid alcohol (4 per cent, in 95 per cent, 

 alcohol) and nitric acid alcohol (3 per cent, in 95 per cent, alcohol) 

 are better than the hydrochloric acid alcohol (Bunge's fluid). 

 Sulphuric acid alcohol acts very slowly especially on bulk tissues, 

 and even Protozoa take twenty-four hours at 35 C. before their 

 masked iron is revealed. Nitric acid alcohol acts more quickly 

 and extracts very little of the iron it liberates (which is a danger 

 with Bunge's fluid) ; the process is completed in about thirty-six 

 hours. 



Sections are treated with acid alcohol, 90 per cent, alcohol, 

 and aq. dest., and then Macallum's hsematoxylin is added ; the 

 sections are washed in aq. dest., stained in safranin, as described in 

 next section, dehydrated and mounted in balsam. 



PRUSSIAN BLUE REACTIONS ON ORGANIC COMPOUNDS. Sections 

 after being treated in the acid alcohol (nitric or sulphuric) are 

 washed in pure 90 per cent, alcohol and then in aq. dest. They 

 are placed not longer than five minutes in the following solution : 

 aq. potassic ferrocyanide 1-5 per cent., and hydrochloric acid 

 0-5 per cent, in aq. solution equal parts, freshly made. Again 

 washed carefully in aq. dest. stained in eosin or safranin, dehy- 

 drated in alcohol, cleared in oil of cedar and mounted in benzole 

 balsam. The safranin or eosin are used in 1 per cent, strength in 

 30 per cent, alcohol, for three minutes for eosin, and for one half- 

 hour for safranin, and differentiated in 90 per cent, alcohol. 



FERRIC AND FERROUS SALTS both occur in inorganic iron com- 

 pounds. Ferrous salts may be distinguished from ferric by the 

 fact that only the latter give an immediate reaction with ferro- 

 cyanide of potassium, while the former react with f erricyanide of 

 potassium. Fix material in alcohol of about 90 per cent, for several 

 days. 



Reaction for Ferric Salts. Wash sections in aq.. dest., transfer 

 to 2 per cent. aq. sol. ferrocyanide of potassium for from three to 

 fifteen minutes. Bring to acid alcohol (1 c.c. in 70 per cent, alcohol) 

 for about ten minutes. The Prussian blue reaction takes place. 

 Wash in pure 70 per cent, alcohol, dehydrate clear and mount in 

 benzole balsam. 



Counter-stain if desired in eosin or safranin (op. cit.). 



Ferrous Salts. As above, substituting ferricyanide of potassium 

 instead of ferrocyanide. 



