Part 60. Non-Poisonous Drugs

Part 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, astringents, fixed oils, and volatile oils. Various other substances of more or less importance occur in certain of the non-poisonous drugs but these need not concern us here, especially as many of them are not yet well understood by chemists.

Mucilaginous Or Gelatinous Substances

Mucilaginous or gelatinous substances form the most important 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 C₁₂H₂₂O₁₁, the same as that of cane-sugar. Prolonged boiling with dilute acid converts arabin into a kind of glucose sugar known as arabinose. A similar substance yielding arabinose forms about half of gum tragacanth, about one-third of the gum being a carbohydrate called tragacanthin (C₆H₁₀O₅) which differs from arabin in being insoluble, although it absorbs water and swells exceedingly. Tragacanth is an exudation from wounds made in the stems of the gum-bearing tragacanth shrub (Fig. 157) and related species. The root of the marshmallow (Fig. 158) contains about one-third of its weight of a mucilage, having the same formula as tragacanthin. The same formula is given also to the mucilage yielded copiously by the outer coat of the flaxseed (Fig. 279). A similar mucilage but with the formula C₁₈H₂₈O₁₄ is obtained in large quantities from the outer coat of quince seed (Fig. 93). The slipperiness of the inner bark of our slippery elm and the closely similar English elm (Fig. 159) is due to the large amount of a mucilaginous carbohydrate which it contains. The pith of sassafras (Fig. 160) yields to hot water a similar mucilage.

The jelly-like constituent of the lichen called Iceland moss (Fig. 161) is a carbohydrate known as lichenin or lichen-starch (C₁₂H₂₀O_io). It is insoluble in cold water but becomes dissolved upon boiling, and forms a jelly when cooled. Lichenin is almost if not quite identical with the gelatinous constituent of carrageen or Irish moss (Fig. 118) which we have already studied. The chief remedial constituent found in the root of the licorice plant (Fig. 162) is a bitter-sweet, yellowish compound forming a jelly with water.

Astringents

The astringents present in vegetable drugs, or extracted from them, are various tannins, significant properties of which have already been described in section 57. As examples of drugs used more or less for their astringency may here be mentioned the root of rhubarb (Fig. 163) and the bark and leaves of witch-hazel (Fig. 164), from both of which fluid extracts and other medicinal preparations are obtained.

As examples of fixed oils much used in medicine for their lubricating or soothing effect, there are in common use the expressed oil of almond, olive-oil, and the oil of cacao seed known as cacao butter, already studied for their food value (in sections 33 and 39); and to these may now be added castor-oil and the oily drug lycopodium. Castor-oil, obtained from the seeds of the castor-oil plant (Fig. 165), is believed not to be taken up by the digestive tract as a food, but to owe its great medicinal value to its lubricant and mildly irritant properties. The sulphur-yellow powder known as lycopodium, obtained from the club moss (Fig. 166), consists of minute bodies called spores by means of which the plant perpetuates its kind. Each spore contains nearly 50% of a fixed oil, and the surface is remarkably repellent of water. A teaspoonful of the spores thrown into a bowl of water will float as a thin layer, and one's fingers may now be repeatedly thrust into the water and withdrawn without becoming wet in the least. Its waterproof nature gives lycopodium some value as an application to moist, inflamed surfaces of the body, and makes the spores useful also as a covering for moist pills to prevent their sticking together. The large amount of fixed oil contained in the spores renders them, moreover, very inflammable, and has led to their use in the manufacture of fireworks, and also as a means of producing artificial lightning in private theatricals.

Volatile oils form the most important constituent of a number of non-poisonous drugs which we have already studied in the last chapter as food-adjuncts; namely, lemon, caraway, anise, cardamoms, spearmint, sage, ginger, and hops. The drugs calamus, asafetida, and saffron are the only others of this class which call for mention here. Calamus consists of the underground stem of the sweet-flag (Fig. 167). It contains about 1% of a volatile oil to which it owes its pleasant aromatic qualities. Asafetida is a gummy substance obtained by drying the milky juice which exudes from the cut roots of the asafetida plant (Fig. 168 I) and related species. Many people regard it when in full strength as about the most ill-smelling of drugs. It is a curious fact, however, that in spite of its odor asafeticla is highly valued as a condiment and extensively used for that purpose in Persia and other oriental countries. Nor is its use as a food-adjunct confined to eastern peoples. Many of us have often relished it in gravies and sauces, little suspecting that the flavor we were enjoying was due to a substance which is ordinarily most repulsive. The volatile oil upon which the odor and flavor of asafetida depend is chemically very similar to the oil of mustard, which as we know is pleasant to eat only in minute quantity. Indeed it is almost always true of food-adjuncts that "a little more than a little is by much too much." The opposite effect upon us of the same substance according as it acts in larger or smaller amount is well illustrated also in very many perfumes, and, as we shall more fully show, in a large proportion of medicines. Saffron consists of the dried stigmas of the saffron crocus (Fig. 168 II). It contains about 7% of a volatile oil of agreeable flavor, and a small amount of a deep yellow coloring matter which however is of remarkable strength. One part of saffron shaken up with 100,000 parts of water gives a distinct yellow tinge. The principal use of the drug is to impart an attractive color and flavor to medicinal preparations. Most of the volatile oils above mentioned are used in medicine mainly for their stimulating effect or for imparting a pleasant flavor to other drugs.