72 MICROSCOPIC TECHNIQUES 



Result. A yellowish deposit of semicarbazones appears in the 

 areas where the aldehydes and ketones are present. 



PURINES 



Tests that have been found to give positive results with all of the 

 purines have the unhappy characteristic of being highly unspecific. 

 Thus the reduction of silver salts is a reaction much too unspecific 

 to merit consideration; Saint-Hilaire's method involving precipita- 

 tion of insoluble copper salts of purines, and the transformation of 

 the copper into its red ferrocyanide is a reaction also given by 

 protamines, histones, and other protein products (Lison 1936, pages 

 183-186) . 



The murexide test, which is positive with uric acid, xanthine and 

 its methyl derivatives, and guanine, is not given by adenine or 

 hypoxanthine (Lison 1936, pages 186-187). This reaction has the 

 disadvantage of being too drastic to permit its use for fine structures 

 and its disintegrating effect on tissue sections presents technical 

 difficulties. However, it may prove useful in some cases and for this 

 reason it will be described. Since it is no different from the xantho- 

 proteic reaction, a yellow-orange color would be indicative of pro- 

 teins, but it should be kept in mind that the xanthoproteic test is 

 not specific for proteins since other compounds, such as alkaloids, 

 benzene derivatives, etc., can also be nitrated in this manner to yield 

 products having the same color. • 



Cowdry (1943, page 196) suggested that the modification of the 

 Courmont-Andre method by Hollande (1931) be used. It enables a 

 more reliable localization of urates in tissue. 



Murexide Test for Certain Purines 



SPECIAL REAGENTS 



Concentrated Nitric Acid. 

 Concentrated Avfimonium Hydroxide. 



PROCEDURE 



1. Prepare sections by any of the usual methods. 



2. Place a drop of nitric acid on a section and warm gently for 

 30 sec. 



