48 Microscopic Histochemistry 



second, it does not precipitate fast enough; and, third, mo- 

 lybdenum blue is very soluble and difiFusible and has a great 

 aflSnity for protein substances.®^ Therefore, the best one could 

 expect of this method would be a diffuse blue coloration 

 around areas of very high concentration of organic phos- 

 phate without any sharpness of localization. The same criti- 

 cism applies to all other methods based on the molybdenum 

 blue principle (Angeli,®^ Serra,®^ and Okamoto®*). 



On the other hand, it might well be possible to develop a 

 histochemical adaptation of Mandel and Neuberg's idea®^ 

 (destroying organic phosphates with strong H2O2). 



Sulfur.— MsLCsllum^^ demonstrates sulfates by treating 

 frozen sections of fresh tissue with a dilute solution of lead 

 acetate, washing them with dilute nitric acid to remove all 

 lead precipitates except acid-insoluble sulfate, and convert- 

 ing the latter with ammonium sulfide to brown-black PbS. 

 Because of the great mobility of sulfate ions, this method 

 should be applied to frozen-dried tissues. 



According to Klein,®^ a number of organic compounds of 

 sulfur are converted to sulfate by strong H2O2. There is a 

 possibility that a histochemical method could be developed 

 on this basis. 



Arsenic— The methods proposed for the demonstration of 

 inorganic arsenic are based either on the formation of As2S3®^ 



61. Bensley, R. R.: Biol. BuU., 10:49, 1908. 



62. Angeli, B.: Riv. di biol., 10:702, 1928. 



63. Serra, J. A., and Queiroz Lopes, A.: Portugal. Acta biol., 1:111, 1945. 



64. Okamoto, K., Seno, M., and Kato, A.: Taishitzu Gaku Zasshi, 13:97, 

 1944. 



65. Mandel, J. A., and Neuberg, C: Biochem. Ztsclir., 71:196, 1915. 



66. Macallum, A. B.: Die Methoden der biologischen Mikrochemie, in 

 Abderhalden's Handb. d. biol. Arbeitsmeth,, V-2:1099 (Berlin and Vienna: 

 Urban & Schwarzenberg, 1912). 



67. Klein, G.: Oesterreich. bot. Ztschr., 76:15, 1927. 



68. Brunauer, S. R.: Arch. f. Dermat. u. Syph., 129:186, 1921; Osborne, 

 E. D.: Arch. Dermat., 12:773, 1925; Memmesheimer, A. M.: Dermat. 

 Ztschr., 54:4, 1928. 



