44 Microscopic Histochemistry 



can be incorporated in the fixative (in the form of Regaud's 

 mixture) or appHed to sections of formaUn- or alcohol-fixed 

 material. Lead is demonstrated in the form of yellow, rather 

 opaque crystals, soluble in dilute nitric acid and blackened 

 by ammonium sulfide. 



This method cannot be used with bones which require de- 

 calcification, since lead chromate is soluble in acids. In bones, 

 lead can be demonstrated by transforming it into brown- 

 black PbS ( Sieber ) ,^^ which is resistant to the action of mod- 

 erately strong acids. The pieces are fixed in formalin satu- 

 rated with H2S, washed, and decalcified with 5-10 per cent 

 trichloroacetic or formic acid. Lead will show up in a dark- 

 brown or black shade, depending on the amount present. 

 However, a number of heavy metals form very similar sul- 

 fides, indistinguishable from that of lead without further 

 identifying tests. 



Theoretically, it should be possible to localize lead by de- 

 calcifying the pieces of bone with 5-10 per cent sulfuric acid 

 containing about the same concentration of sodium or am- 

 monium sulfate. Under such conditions lead would be trans- 

 formed into white, insoluble lead sulfate, which could then 

 be identified in the form of the sulfide. Other heavy metals 

 would not interfere. 



Mercury.— The forms in which mercury may occur in the 

 tissues are poorly known. Judging from the reactions de- 

 scribed for its identification, it appears to be rather loosely 

 bound and reactive. 



Brandino^^ suggests the use of diphenylcarbazide as a re- 

 agent but does not give any detailed instructions. Okamoto^^ 

 uses diphenylthiocarbazide or diphenylthiocarbazone (dithi- 



49. Sieber, E.: Arch. f. exper. Path. u. Pharmakol., 181:273, 1939. 



50. Brandino, G.: Studi Sassari, 5:85, 1927. 



51. Okamoto, K., Seno, M., and Okumura, T.: Taishitzu Gaku Zasshi, 

 13:89, 1944. 



