30 MICROSCOPIC TECHNIQUES 



ARSENIC 



Castel ( 1934-1935a, 1936) developed two methods for the histo- 

 logical localization of arsenic. In one the tissue is fixed in an abso- 

 lute alcohol-chloroform-hydrochloric acid mixture saturated with 

 hydrogen sulfide, and the appearance of yellow granules was be- 

 lieved by Castel to be due to the formation of arsenous sulfide. A 

 reinvestigation of this technique by Tannenholz and Muir (1933) 

 led them to conclude that the yellow granules formed were not re- 

 lated to the presence of arsenic but were more likely composed of a 

 sulfur-protein complex. 



The other method of Castel was based on the precipitation of 

 either cupric hydrogen arsenite (Scheele's green) or the cupric ace- 

 tate-cupric arsenite double salt ( Schweinf iirter green), and this pro- 

 cedure appears to be a reliable one. 



Castel Cupric Salt Method for Arsenic 



SPECIAL REAGENTS 



Formalin-Copper Salt Reagent. Add 2.5 g. cupric sulfate or neutral 

 cupric acetate to 100 ml. metal-free 10% formalin (hydrogen sul- 

 fide is used to test for traces of metals in the formalin). 



PROCEDURE 



1. Place small pieces of tissue in the formalin-copper salt reagent 

 for 5 days. 



2. Wash tissue in running water for 1 day. 



3. Prepare paraffin sections as usual and examine after re- 

 moval of the paraffin. 



Result. Green granules are indicative of arsenic. 



BISMUTH 



The histochemical detection of bismuth is founded on the reaction 

 of Leger ( 1888) , which is the precipitation of the double iodide of 

 bismuth and an alkaloid. Komaya (1925) and Christeller (1926) 

 employed the quinine salt for their tissue studies, and later Castel 

 ( 1936) suggested the use of the brucine salt to avoid the interfer- 

 ence of iron which plagues the quinine method. He also modified 

 the earlier procedures by substituting sulfuric for nitric acid in the 

 reagents, Castel ( 1934-1935b), a change which enables the visual- 



