PURINES, INDOLE AND RELATED COMPOUNDS 73 



3. Drain off the acid by means of blotting paper and add a drop 

 of water, which is also removed in the same way. 



4. Expose the section to ammonia vapors. 



Result. A purple-violet color is a positive test for uric acid, 

 guanine, and xanthine and its methyl derivatives. A yellow-orange 

 color is usually indicative of protein material. The effect of diffus- 

 ibility should be considered in the interpretation of localizations. 



HoUande Modification of Courmont-Andre Method 

 for Uric Acid and Urates 



SPECIAL REAGENTS 



Silver Nitrate-Neutral Formalin Fixative. Equal vol. of 1% silver 

 nitrate and 4.4% formalin (neutralized with calcium carbonate) 

 mixed just before using. 



0.5% Phosphomolyb die Acid. 



PROCEDURE 



1. Fix tissue in silver-formalin mixture for 12-24 hr. in the dark. 



2. Wash for 24 hr. in several changes of distilled water. 



3. Prepare paraffin sections. 



4. Stain sections with hemalum for 10 min. and wash in running 

 tap water for 30-60 min. 



5. Place in 1 % aqueous orange G or eosin 30-60 min. and wash 

 rapidly in distilled water. 



6. Treat with the phosphomolybdic acid soln. and wash in dis- 

 tilled water. 



7. Stain with 0.12% aqueous light green for 1-10 min. 



8. Differentiate quickly in 95% alcohol, dehydrate in isoamyl 

 alcohol, clear in xylol, and mount in balsam. 



Result. Urates will appear black, chromatin blue, protoplasmic 

 inclusions red to orange, and collagenic fibers green. 



INDOLE AND RELATED COMPOUNDS 



Lison (1936, pages 160-162) lists five reactions for the histo- 

 chemical detection of compounds containing the indole structure. 

 All of the tests leave much to be desired; their specificity is rather 



