EMPLOYMENT OF MICROCHEMISTRY 369 



may be left over night in hydrochloric acid lo parts and water 

 90 parts and then remounted in chloral hydrate. This clears 

 up very refractory subjects. See also page 293. 



When the sections are in condition to show all of the cells 

 clearly make camera lucida drawings (see page 280) from both 

 cross and longitudinal sections, showing groups of cells from each 

 tissue to compare with similar drawings from the powder un^der 

 investigation. This method of comparison is much more reliable 

 than one in which the drawings are not made. If. the full length 

 of the bast fibers cannot be seen in the sections the fibers can be 

 isolated by the methods for maceration given in Chapter XVI 

 under Maceration. 



Employment of Microchemistry. — Having thus become 

 acquainted with the different tissues mount a section in chloral 

 hydrate iodine (see page 292) to bring out clearly any starch 

 that may be present. This reagent dissolves proteids and swells 

 the starch-grains and colors them blue so that they can easily be 

 seen even when very minute and previously obscured by the cell- 

 contents. Drawings had better be made of the starch grains, 

 but since they are swollen in the chloral hydrate other sections 

 mounted in potassium iodide-iodine (see page 311) should be 

 used for the drawings. Other sections should be tested for aleu- 

 rone (page 330), gums (page 348), mucilage (page 352), resins 

 (page 360), and tannins (page 364). 



The nature of the cell-walls is next to be tested. Mount sec- 

 tions in chloroiodide of zinc (page 292), and stone cells, bast 

 fibers, and cork cells should be colored yellow; and the walls of 

 other tissues should be purple, indicating cellulose. Mount sec- 

 tions in phloroglucin (page 324), and bast fibers and stone cells 

 only will be colored pink; while other sections mounted in aniline 

 sulphate (page 287) will have yellow bast fibers and stone cells 

 and all other tissues unstained. Phloroglucin and aniline sul- 

 phate, since they stain only lignified walls, are of especial value 

 in sharply differentiating stone cells, bast fibers, and wood fibers 

 and the tracheal tissues from all other tissues. 



Finally the sections are to be studied with a polariscope (page 

 24 



