NON-POISONOUS DRUGS 163 
The number of plants which have been used medicinally is 
enormous. Many of these, however, have been found to be 
either so dangerous in their action or of so little value that 
they are now used if at all only by the ignorant. Neverthe- 
less, the number of those still used in scientific medicine is 
rather large. Numerous also are the poisonous plants known 
to botanists. Plainly, in the present chapter only a small pro- 
portion of these can be considered. The ones chosen are 
typical examples of those classes of medicinal and poisonous 
plants about which it is most important for a beginner to 
-know. The medicinal plants are thus divided: (a) those 
yielding non-poisonous drugs, and (b) those yielding poisonous 
drugs. Poisonous plants are grouped into (a) those dangerous 
to eat and (b) those dangerous to handle. 
60. Non-poisonous drugs include various substances which 
may be more or less nutritious, stimulating, or irritating, 
or may be useful for their soothing influence upon inflamed 
surfaces, or for some other mild healing virtue. Some of the 
substances here included under this heading may perhaps 
under extraordinary conditions act as poisons; what is meant 
by calling them non-poisonous is that much larger quantities 
than are generally used would be required to produce any 
harmful effects under all ordinary circumstances. 
The chemical compounds upon which their value mainly 
depends include mucilaginous or gelatinous constituents, as- 
tringents, fixed oils, and volatile oils. Various other sub- 
stances of more or less importance occur in certain of the non- 
poisonous drugs but these need not concern us here, es- 
pecially as many of them are not yet well understood by 
chemists. 
Mucilaginous or gelatinous substances form the most im- 
portant part of the drugs known as gum arabic, tragacanth, 
marshmallow, flaxseed, quince seed, elm bark, sassafras pith, 
Iceland moss, Irish moss or carrageen, and licorice root. 
Gum arabic is an exudation from the trunk and branches of 
the gum arabic tree (Fig. 156) and related species. When 
pure the gum consists essentially of a carbohydrate called 
arabin, the formula of which is C;,.H.2On, the same as that 
of cane-sugar. Prolonged boiling with dilute acid converts 
