36 MICROSCOPIC TECHNIQUES 



PROCEDURE 



1. Prepare frozen sections of fresh tissue. 



2. Place 1-2 drops of hot Nitron reagent on a cover slip, and 

 place the cover slip over the section on a glass slide so that the tissue 

 is bathed in the liquid. 



3. Put in a refrigerator for 30 min. to aid in the crystallization of 

 the nitrate. 



4. Examine with polarized light under a microscope immediately 

 on removal from refrigerator. 



Result. The doubly refractive zones are due to the insoluble 

 nitrate. 



SULFHYDRYL AND DISULFIDE GROUPS 



The earlier literature dealing with the application to tissue sec- 

 tions of the nitroprusside reaction for sulfhydryl groups, and the 

 reduction of disulfide compounds to give this test, has been 

 reviewed by Lison (1936, pages 133-136). The procedure given by 

 Pv,apkine and recommended by Lison, as well as the methods of 

 Bourne (1935) and of Hammett and Chapman (1938-1939), will 

 be given. The latter investigators critically examined the nitro- 

 prusside test and concluded that it should not be considered a 

 quantitative reaction; they established a well-defined procedure 

 which they believe most likely to yield satisfactory qualitative 

 results. However, the problem of diffusibility will no doubt limit, 

 or eliminate, the use of any nitroprusside method. 



Nitroprusside Test of Rapkine 



SPECIAL REAGENTS 



5% Sodium Nitroprusside. For plant tissues. 



2% Sodium Nitroprusside. For animal tissues. 



Ammonium Sidjate Crystals. 



Cone. Ammonium Hydroxide. 



10% Potassium Cyanide. 



10% Trichloroacetic Acid. 



5% Zinc Acetate. 



PROCEDURE 



A. For free sulfhydryl groups 



