CHAPTER VI 

 INORGANIC SUBSTANCES 



Inorganic constituents occur in tissues in three forms: (1) 

 soluble, diffusible, and, for all practical purposes, completely 

 ionized; (2) insoluble but readily convertible into the solu- 

 ble form; and (3) incorporated into complex, soluble, but 

 poorly diffusible or insoluble organic molecules. The last 

 form is often called "occult" or "masked" because the regular 

 reactions of the inorganic part are not obtainable unless the 

 organic matrix is first more or less completely destroyed. 



Diffusible substances can be localized only by the use of 

 the freezing-drying method. Even so, localization is often 

 only approximate on account of their high mobility, causing 

 noticeable displacement of the solute before quantitative 

 precipitation by the reagent can take place. 



Some substances of the second group are capable of giving 

 direct ionic reactions without being dissolved first; others 

 must be treated with acid to make them soluble. In the latter 

 case the reagent must be present in the acid from the very 

 beginning, to bind the ions as fast as they are formed in the 

 course of solution. 



The demonstration of "masked" constituents presents 

 considerable diflBculties. Unmasking agents, with a few ex- 

 ceptions, are quite harsh chemicals (or intense heat) which 

 may destroy tissue architecture beyond recognition. 



A. METALLIC ELEMENTS 



Sodium.— No method is available for the demonstration of 

 this element. The demonstration of "sodium chloride" by the 

 AgNOs technique^ is such a naive idea that it does not de- 

 serve serious consideration. 



1. Seeger, P. G.: Ztschr. f. mikr.-anat. Forsch., 53:65, 1943. 



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