CHAPTER X\'I 

 REAGENTS AND PROCESSES 



The different kinds of cell-walls and cell-contents may be 

 demonstrated by the use of reagents which, in some cases, im- 

 part characteristic colors to walls and contents; in other cases 

 act as selective solvents, dissolving some of the walls and con- 

 tents, leaving others undissolved; or the reagents may produce 

 precipitates the nature of which furnishes good evidence regard- 

 ing the character of the substance which has united with the 

 reagent to produce the precipitate. 



These reagents together wnth their uses, will now be given in 

 alphabetical order. 



Acetic Acid dissolves most ethereal oils, while most fatty 

 oils are insoluble in it; dissolves calcium carbonate with evolu- 

 tion of CO,, while calcium oxalate is unaffected by it^ and it 

 therefore serves to distinguish between these two salts of cal- 

 cium; solvent of crystals of hesperidin which have been depos- 

 ited from the cell-sap of oranges, etc., when these have lain 

 for some time in alcohol; when various lichens are treated with 

 it, crystals of calycin in acicular form are deposited after the 

 lichens thus treated have been powdered and dried; i per cent, 

 solution dissolves globoids in aleurone grains, while any crystals 

 of calcium oxalate present are unaffected by it; when pieces of 

 potatoes, carrots, etc., are macerated in it, the separate cells 

 become isolated. Used in the preparation of various fixatives. 



Albumen. — The white of egg is u.sed with an equal amount 

 of glycerine and a trace of salicylate of soda for fixing micro- 

 tome sections to the glass slide, the sodium salicylate acting 

 partly as an antiseptic. (Page 263). 



Alcannin. — This is a coloring matter, obtained from the 

 roots of Alcanna tincloria. A tincture of alcannin to be used 



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