Organic Substances 131 



immediate disappearance of fluoresence on the addition of 

 hydrosulfite to the mounting medium. 



Lewisite 



Lewisite, a war gas, is a mixture of chlorovinylarsins. In 

 an alkahne medium it decomposes to yield acetylene; the 

 latter will precipitate cuprous ions in the form of red copper 

 carbide. This reaction is utilized for the histochemical dem- 

 onstration of lewisite. 



Method^ 



Prepare three stock solutions: A, an 8 per cent solution of 

 cupric sulfate in distilled water; B, a 20 per cent solution of 

 sodium sulfite in distilled water; C, a solution of 50 g. of 

 sodium thiosulfate and 20 g. of sodium hydroxide in 80 ml. 

 of distilled water to which 1 ml. of piperidine has been 

 added. The latter enhances the red shade of the precipitate. 

 For use, mix 10 ml. each of solutions A and B; when clear, 

 add 10 ml. of solution C. The mixture is unstable and can be 

 used for only about 1 hour. 



Dip frozen sections of fresh tissue in the reagent for a few 

 seconds; wash them, dehydrate in alcohol, and mount in bal- 

 sam. Counterstaining is not recommended. This is an un- 

 tested method. 



"Mustard" (Dichlorodiethylsulfide) 



Gold chloride reacts with mustard to yield a bright yellow 

 complex, which can be reduced to black metallic Au. 



Method^ 



Immerse frozen sections of fresh tissues in a 1 per cent 

 solution of gold chloride for 2-3 minutes. Mount on a slide, 

 flood with 5 per cent sodium hydroxide for 30 seconds. Wash, 

 dehydrate, and mount in balsam. Shades of black and 



2. Ferguson, R. L., and Silver, S. D.: Am. J. Clin. Path., 17:37, 1947. 



3. Silver, S. D., and Ferguson, R. L.: Am. J. Clin. Path., 17:39, 1947, 



