Inorganic Substances 33 



for the anthraquinone lakes, eosin for gallamin blue ) should 

 be used, because basic dyes may be adsorbed to sites previ- 

 ously stained by the lake, giving dark, murky shades. 



The method described by Cretin^- is quite specific and 

 gives very sharp pictures; how^ever, the preparation of the 

 highly unstable reagent is difficult. The method is so ca- 

 pricious as to be a curiosity rather than a dependable test. 



Since in animal tissues almost all insoluble Ca is in the 

 form of phosphate and carbonate and, conversely, practi- 

 cally all insoluble phosphate and carbonate are Ca salts, any 

 method which demonstrates these two anions is reasonably 

 specific for Ca. With plant tissues, which may contain large 

 amounts of Mg phosphate, this does not hold. 



The phosphates and carbonates of almost all heavier 

 metals are insoluble, and many of them are convertible into 

 intensely colored compounds. Thus there is a wide choice 

 of reagents, as enumerated by Stoeltzner.^^ To mention a 

 few: Ag-> metallic Ag (black); Co->CoS (black); Cu-^ 

 Cu2Fe(CN) 6 (red-brown); Fe++ -^-Fe3++ (Fe+ + + [CN]6)2 

 (TurnbulFs blue); etc. Of these, only the silver technique 

 is employed extensively, although at times the others may 

 also be useful, especially when a shade other than black is 

 desired. 



The silver technique ( Salge and Stoeltzner,^* Kossa^^ ) . 



Method 



Before using the silver solution, rinse the slide thoroughly 

 in distilled water. Immerse the slide for 5-10 minutes in a 

 0.2-1 per cent solution of AgNOs. At the sites of Ca phos- 

 phate-carbonate the corresponding silver salt, yellowish in 

 color, will form. This can be reduced to metallic silver either 

 by exposing the jar to direct sunlight (or to the light of an 



12. Cretin, A.; Bull, d'liistol. appliq. a la physiol., 1:125, 1924. 



13. Stoeltzner, W.: Virchows Arch. f. path. Anat., 180:362, 1905. 



14. Salge, B., and Stoeltzner, W.: Berl. klin. V^^chnschr., 37:298, 1900. 



15. Kossa, J. von: Beitr. z. path. Anat. u. z. allg. Path., 29:163, 1901. 



