The Curing of Leaf Drugs with Special Reference to their Appearance.*

By R. H. True and W. W. Stockberger.

At the present time it is certain that many more crude drugs are bought and sold on their appearance than on their tested physiological properties. It is, therefore important for any grower or collector of crude drugs that he should strive to obtain sightly articles. In this discussion especial attention is given to leaf drugs since it is more difficult to obtain the desired appearance in leaves than in other types of crude drugs of vegetable origin.

The appearance of a crude leaf drug is dependant on (1) the wholeness of the leaf and (2) on the color. The degree to which the leaf may be broken is largely dependant on the amount of moisture present. Stramonium leaf, and many other kinds, when containing less than 5% of water are apt to be brittle. If too dry care in handling will do but little to preserve the leaf in an unbroken condition.

The color of the leaf is in general dependant on the green coloring matter known as chlorophyll. Chlorophyll is found in the superficial parts of plants impregnating minute colorless granules. Experiments have shown that light, while necessary in general for the formation of this green pigment, when present in too great intensity breaks it down, the result being a substance having a yellowish-green color. Chlorophyll is also decomposed by the action of acids even in considerable dilution with the result that a somewhat similar yellowish-green color is developed.

In addition to the chlorophyll bodies the cells of fresh leaves contain a large number of chemical compounds of whose nature very little is known. Many of them are in all probability extremely unstable and out of reach of the present methods of chemistry. Since the juice of fresh crushed leaves is markedly acid, we know that a considerable amount of one or more acids is present. In all probability many active principles exist in these cells in a dissolved. state. From the evidence now at hand, it appears likely that many substances capable of reacting when brought together under proper

* Read at Kansas City meeting, A. Ph. A., 1904.

conditions exist in a dissolved state in the cell at the same time without any such reactions taking place. Indeed, some investigators have asserted that a single living cell may contain at one time both an acid and an alkali so isolated as to prevent their coming into contact with each other. This isolation is brought about by the enclosing of the dissolved substances in separate vacuoles surrounded by their membranes of protoplasm. According to this explanation, the substances are kept apart by special membranes of living material. It has been shown for tannins and several other principles that such a method of isolation is maintained.

It is also probable that enzymes of different kinds, located at such points as the activities of the plant may determine, are found in the cells of fresh leaves. Among these enzymes those carrying out oxidizing processes are of significance in connection with the preservation of the bright color of leaf drugs. Those enzymes known as oxidases are able to use the oxygen of the air in bringing about the oxidation of tannins and other compounds with the development of brown products.

It is clear from these considerations that there are stored in the living cell various substances capable when mingled of producing bodies which have an unfavorable effect upon the green color of the leaf drug. The presence of moisture in quantities sufficient to readily support chemical reactions is necessary to all of these changes.

The most conspicuous modification that marks the drying out of a leaf is the loss of water and the consequent shrinkage in bulk. A leaf may lose water up to a certain point and yet the cells constituting it may not be killed. When, however, the water loss goes beyond this point the structure of the most unstable substance, the living protoplasm, seems in some way to be injured and the protoplasm, like the copper sulfate crystal from which the water of crystallization has been removed, falls to pieces. This means the destruction of the protoplasmic layers surrounding the vacuoles in which the various isolated compounds are held, and the consequent permeability of these retaining membranes. Should the enclosed substances now diffuse together they will react according to the degree of mixture. The only practicable way to check these reactions is to continue the drying process until there is not enough moisture left to support them. Thus, further drying would tend to limit the undesirable changes initiated by the previous stage of desiccation.

Two classes of reactions are likely to result in detriment to the appearance of the drug: (1) the acid solutions of the cell by acting on the chlorophyll tend to give the product a yellowish color; (2) the oxidizing enzymes acting on the tannins and other oxidizable compounds present give the product a brownish color. When, in curing a leaf drug, it fails to lose water steadily, especially during the earlier stages, enough moisture is retained to support not only the action of the acids on the chlorophyll, but, more important still, the action of the oxidases on the oxidizable substances present, the development of a more or less marked brown color ensuing. Hence, the necessity of maintaining a steady loss of water from the leaf, especially in the earlier stages of curing.

In curing drugs by artificial heat, if the temperature to which the fresh leaf is exposed exceeds about 50° C., a cooked appearance results, accompanied by a darkening of the leaf. This may be explained, at least in part, by what has already been indicated. The protoplasm is kiled by the action of the heat and reacting compounds are freed from their isolating vacuoles in the presence of an abundance of moisture. Consequently, chemical reactions take place with great freedom, resulting in the relatively complete action of the acids with the chlorophyll and in the more prolonged action of the oxidases on the contents of the cells, both of which processes injure the color of the drug.

The following practical rules for the curing of leaf drugs may here follow by way of summary. Cure leaf drugs in such a way that the water loss is steadily maintained during the process. Dry until a degree of desiccation is reached which shall inhibit chemical reactions.

If artificial heat is used, be careful not to heat the fresh leaf to such a degree as to thereby injure the protoplasm since the death of the cells should be brought about only through water loss.

After the protoplasm has been killed carry on desiccation more rapidly until chemical reactions are inhibited. Should the leaf be collected for its volatile oils, keep the temperature low but do not fail to secure a steady water loss.

Since strong sunlight changes chlorophyll to a greenish-yellow substance, avoid too long exposure to sunlight.

Bureau of Plant Industry, U. S. Department of Agriculture,
Washington, D. C.

Historical Fragments.

By Edward Kremers.

8. Borneo Camphor.

The tree, Dryobalanops camphora, from which this variety of camphor, also known as Barus camphor or Malayan comphor, is derived, is reported to be "one of the most majestic objects of the vegetable kingdom." The tall trunk, round and straight, rises to a height of from 100 to 150 feet without a branch. It then spreads into a dense crown of shining foliage, 50 to 70 feet in diameter, on which are scattered beautiful white flowers of delicious fragrance.

Although this tree has long attracted the attention of scientists, not only on its own account, but also because of the camphor which it yields, very little is known about it chemically. A careful investigation of the volatile constituents from the several parts of the tree would make an interesting phytochemical study.

The collection of the camphor from the crevices of the trunk is, no doubt, an old practice. That the tree occasionally contains reservoirs filled with an oil, also seems to have been long known. Thus e. g. Ibn Khurdadbah in the ninth century mentions that the oil is collected from the reservoirs. A sample of such an oil, collected by Motley from a felled tree in 1851, was examined. It is stated to have been like turpentine oil holding some borneol and resin in solution. An oil examined by Lallemand and brought by Junghuten from Sumatra, where it had been prepared by distillation from various comminuted parts of the tree, is reported to have been devoid of borneol.

It is this borneol or Borneo camphor which has been of interest to oriental travelers. It is found deposited in longitudinal fissures in a solid crystalline state and can only be collected by the destruction of the entire tree. While it is commonly known that this camphor is used in funeral rites, it may be known to but few, if any, pharmaceutical students what rites are observed in its collection. For a description of these rites as practiced by the Borneo head-hunters we are indebted to W. H. Furness, who has lived for several months.