36 VEGETABLE DRUGS WITHOUT ORGANIC STRUCTURE. 



In the market three kinds are handled — leaf or flake, 

 consisting of the whitest, flattest pieces, most valuable; 

 stem, or worm-like pieces ; and sorts, or smaller rounded 

 pieces. The finer leaf tragacanth usually comes from 

 Asia Minor. A particularly fine variety of the stem 

 tragacanth is frequently termed vermicelli. Sorts are 

 usually small exudates or broken pieces of stem and flake. 



Microscopically numerous cells may be seen in various 

 stages of retrograde metamorphosis, their cell walls 



Fig. 3. — Tragacanth. 



Microscopical view of gum tragacanth: s, s'. Remains of starch-grains; 



z, remains of cell-walls (Wiesner). 



being swollen in various stages and undergoing the 

 mucilaginous modification. These are mixed with starch 

 grains, which are simple or compound, and measure four 

 to fifteen microns in diameter. Good microscopical 

 pictures can be obtained best from small tear-like pieces. 

 The larger, better sorts often show no trace of histological 

 structure. The tragacanth should be permitted to swell 

 but slightly in order to best bring out its structure. 

 Chemistry. — Tragacanth consists of varying proper- 



