Inorganic Substances 35 



is very limited. The protein error is very marked in the case 

 of native proteins (unfixed tissues), whereas after a good fix- 

 ation it is usually negligible unless the slide is exposed to the 

 heavy-metal salt for many hours or even days. 



The intense blue staining of calcified structures, such as 

 bone matrix, by various hematoxylin lakes (hemalum, iron, 

 and chrome hematoxylin) is not specific for any component 

 of bone salt.^^ Neither Ca carbonate nor phosphate will stain 

 with hematoxylin; on the other hand, bone matrix will stain 

 even after complete removal of bone salt by a strong acid. 

 The afiinity of bone matrix for hematoxylin lakes is due to 

 the chemical constitution of the organic framework (pres- 

 ence of mucopolysaccharides?), specifically, to its ability to 

 bind the metallic component. 



Masked Ca (mainly in cell nuclei) can be demonstrated 

 only by microincineration. 



Barium and strontium.— Wa.terhouse^'^ recommends a solu- 

 tion of sodium rhodizonate in distilled water or in a buffer of 

 pH 7 as a reagent for Ba and Sr. These two ions give red- 

 brown precipitates with rhodizonate. According to the au- 

 thor, the reaction with Ba can be prevented or abolished, 

 respectively, by treating the section with a solution of sodium 

 chromate; the reaction with Sr is not affected. 



The specificity of this test requires confirmation. Water- 

 house finds that, under the conditions specified, Ca will not 

 react. This is not entirely correct; both bone salt and freshly 

 precipitated pure Ca phosphate stain in a distinct ochre 

 shade with rhodizonate. It is questionable whether Ba and 

 Sr can ever be recognized by the rhodizonate test in the 

 presence of excess Ca. Furthermore, it is known^* that Pb 



16. Schuscik, O.: Ztschr. f. wissensch. Mikr., 37:215, 1920; Cameron, 

 G. R.: J. Path. & Bact., 193:929, 1930. 



17. Waterhouse, D. F.: Nature, 167:358, 1951, and Australian J. Scient. 

 Research, B, 4:145, 1951. 



18. Feigl, F.: Chemistry of specific, selective, and sensitive reactions 

 (New York: Academic Press, 1949). 



