32 MICROSCOPIC TECHNIQUES 



2. Treat the tissue on the slide for a few sec. with several drops 

 of 30% hydrogen peroxide to remove the black sulfide color. 



3. Wash well in tap water and place in the Castel reagent for 1 hr. 



4. Transfer to the diluted Castel reagent and shake gently to re- 

 move precipitates. 



5. Remove most of the liquid from the slide by careful blotting 

 and mount in the levulose soln. 



Result. Bismuth is indicated by the orange-red deposit. The 

 color may darken on standing. (If a counterstain is desired, stain 

 for 4 min. with the counterstain soln.) 



Castel Method for Bismuth 



SPECIAL REAGENTS 



Bismuth Reagent. With the aid of warming, dissolve 1 g. brucine 

 in 100 ml. distilled water containing 3-4 drops of sulfuric acid 

 and add 2 g. potassium iodide. As an alternate reagent dissolve 

 1 g. brucine and 2 g. potassium iodide in 100 ml. of a mixture of 

 equal vol. alcohol and chloroform, 



PROCEDURE 



1. Fix the tissue in 10% formalin and prepare paraffin sections. 



2. Treat deparaffinized sections for 15 min. with the bismuth 

 reagent and wash well in distilled water. 



3. Mount in syrup of Apathy (heat equal parts of paraffin, m.p. 

 60°, and Canada balsam). 



Result. Red granules are indicative of bismuth. 



CHLORIDE AND PHOSPHATE-CARBONATE 



Earlier methods for chloride, including Macallum's ( 1908) silver 

 test, were subject to the difficulty that, in the course of the manipu- 

 lations, a shift in the topographical distribution of chloride oc- 

 curred. Distortion due to this cause can be minimized by applying 

 the freezing-drying process to the tissue before further treatment. 

 Gersh ( 1938) makes use of this fact in his procedure, which enables 

 a differentiation between the chloride in the tissue and the phos- 

 phate and carbonate present. Phosphate and carbonate are visualized 

 together in this method. Two reagents are used, one permits visuali- 

 zation of chloride specifically by effecting the maximum precipita- 



