34 MICROSCOPIC TECHNIQUES 



With the dark field the silver granules appear orange or rust colored. 

 Reagent 1 gives a test for chloride only. Reagent 2 gives a test for 

 chloride plus phosphate and carbonate. 



IODIDE 



A critical study of histochemical methods for the localization of 

 iodides in tissues was presented by Gersh and Stieglitz ( 1933) . After 

 a careful examination, these authors conclude that none of the pro- 

 posed methods is satisfactory. The difficulty is that any precipitat- 

 ing agent that might be used to fix iodide will also precipitate the 

 proteins and hence prevent its proper penetration into the tissue. 



PHOSPHATE 



Microscopic techniques for the detection of phosphorus in tissues 

 are usually based on reactions designed to visualize the phosphate 

 ion. Hence phosphate in organic combination must be liberated be- 

 fore it can be detected. Lison (1936, pages 113-1201 critically re- 

 viewed the various methods and considered Angeli's procedure to be 

 highly specific; this is a molybdate method using stannous chloride 

 as the reducing agent. Serra and Queiroz Lopes (1945) employed a 

 molybdate reaction with benzidine which they report to give a more 

 intense color than that developed by stannous chloride, and they 

 also use a more dilute acid medium, which is less damaging to the 

 tissue. 



Johansen ( 1940, page 198) stated that phosphate may be identi- 

 fied in plant tissues by treating a section with a drop of solution pre- 

 pared by adding 25 ml. saturated magnesium sulfate and 2 ml. satu- 

 rated ammonium chloride to 15 ml. water. Crystals of magnesium 

 ammonium phosphate should form in the presence of phosphate. This 

 procedure is doubtlessly less advantageous than those previously 

 mentioned. 



The method for visualization of enzymatically liberated phosphate 

 (page 78) may also be applied in certain instances. 



Serra and Queiroz Lopes Modification of the Molybdate 

 Method for Phosphate 



SPECIAL REAGENTS 



Acetic Alcohol-Formalin Fixative. Add a few drops of glacial 



