16 MICROSCOPIC TECHNIQUES 



PROCEDURE 



1. Fix tissue in neutral formalin and prepare paraffin sections 

 as usual. 



2. Immerse deparaffinized sections in Siena orange soln. for 2 

 min. 



3. Transfer to 10% hydrochloric acid for 3 min. 



4. Wash twice in distilled water for 10 min., blot with filter 

 paper, and dry at 37°. 



5. Mount in thickened cedar oil. 



Result. Potassium is demonstrated by an orange color on a pale 

 yellow or colorless background. The author of this method has 

 failed to consider the effects of potassium diffusion when aqueous 

 solutions are employed for fixation, etc. Modification of the pro- 

 cedure to obviate this difficulty would be essential. 



CALCIUM 



A critical survey of histochemical tests for calcium was pre- 

 sented by Cameron (1930), who concluded that none of the tests 

 can be considered wholly specific. In all cases calcium must be 

 converted to an insoluble salt, if it is not already present as such, 

 and the insoluble compound is identified directly or it is made more 

 easily detectable by staining or conversion to a colored compound. 

 For visualization of calcium in the form of phosphate or carbonate 

 see page 78. In addition to these tests the Cretin (1924) gallic 

 acid color test has been extensively used, as has the formation of a 

 red precipitate by reaction of calcium salts with sodium alizarin 

 sulfonate (Pollack, 1928). For plant materials it is often sufficient 

 to produce and identify crystals of the oxalate, carbonate, or sulfate 

 (Lee's Vade Mecum, pages 293 and 668). The old test of von Kossa 

 (1901), depending on the reduction of silver salts under bright 

 light, has been championed by Gomori ( 1945a) . While this method 

 will demonstrate inorganic deposits in general, it can be considered 

 specific for calcium in bone or cartilage because the calcium salts 

 are the only ones present in significant amounts. An adaptation 

 of the von Kossa test to bone has been described by McLean and 

 Bloom«( 1940) and Bloom and Bloom ( 1940) . 



