72 POWDEKED VEGETABLE DRUGS 



the clearing up process and to remove air bubbles from the tissues 

 heat should be applied, but the student must bear in mind the changes 

 that heat produces in cell-contents, as starch granules, fats, inulin 

 coloring substances and some other contents. Fortunately, the crys- 

 tals of calcium oxalate remain unaltered. A concentrated solution 

 of potassium hydrate and of sulphuric acid may prove useful as some 

 drugs give characteristic color reactions with these reagents. Feh- 

 ling's solution may be found useful in developing the sugar reaction. 

 The following is a tabulation of the color reactions of the different 

 vegetable elements with chloriodide of zinc. A drop of the reagent is 

 to be added to the section or pinch of powder and the slide mount 

 examined immediately in order that all of the color changes may be 

 noted. 



I. Cell-walls. 



1. Cork. No reaction. 



2. Epidermis, not suberized or lignified. Reaction as for 

 parenchyma. 



3. Parenchyma. A gradual change from reddish brown to 

 deep violet. Reaction may require several hours to 

 develop fully. Reaction due to cellulose. 



4. Bast. As for parenchyma. Reaction more rapid. 



5. Collenchyma. As for bast. 



6. Sieve tissue or phloem. As for bast. Reaction more 

 rapid. 



7. Lignified cells (tracheids, vessels or ducts, wood cells, 

 some bast, sclerenchyma and other lignified elements). 

 Reddish brown reaction, which gradually deepens. Reac- 

 tion due to lignin. 



II. Cell-contents. 



1. Starch. As for parenchyma. The reaction is, however, so 

 rapid that the reddish brown coloration is rarely noticeable. 



2. Protoplasm and proteids. Reddish brown. 



3. Tannin globules. Reddish brown. 



4. Laticiferous fluid. Wine red. 



5. Amylodextrin granules. Reddish brown. 



6. Crystals. No reaction. 



7. Oils and fats. No reaction. 



8. Resin and waxes. No reaction. 



9. Mucilage and gums. No reaction. 

 10. Sugar and inulin. No reaction. 



We shall give a few tests which have proven useful in the examina- 



