A.—Methods For Identification
(Part IV. Powdered Drugs.)
Vegetable drugs frequently, perhaps in the majority of cases, reach the pharmacist in the form of powders, and it is necessary not only to identify them, but to determine their quality in this form. The old and laborious method of making powders in small quantities, by the pharmacist in his own store, has been supplanted by the specialized industry of drug milling. Thus it is that adulteration is made easier and its detection more difficult. Formerly it was considered sufficient for identification of vegetable drugs to describe gross characteristics, such as, color, odor, taste, and such other characteristics as might be brought out by hand lens; but this method is wholly inadequate, and a more detailed examination, microscopical and chemical, now is required. The enforcement of the drug and food laws will require workers skilled in microscopical technique.
Pulverization and Powdering.—Prerequisite to the microscopical study of vegetable powders is a knowledge of the processes of pulverization and drug mills, such as may be found in any well illustrated work on pharmacy, and elements of plant anatomy.
The degree of fineness of the powders is of first importance in microscopical examinations. Coarse powders can not be used and if they are too fine the fragmentary tissues and products are too small to be recognized. These degrees of fineness are represented by certain numbers. A No. 80 powder, as defined by the U.S.P. VIII, for example, is one that will pass through a sieve having 80 meshes to the inch. In the U.S.P. IX No. go powder is defined as "Very fine powder, has a fineness in diameter of particles less than 0.17 millimeters," and it is specified also that the larger proportion of this must not pass through a sieve of lower degree of fineness (See U.S.P. IX, Part II). To obtain the best results, microscopically, powders may vary in fineness from No. 60, a fine powder, to No. 80, a very fine powder.
During the process of pulverization the less resisting tissues, such as thin-walled parenchyma cells, which, for the most part, contain starch, proteids and crystals, are reduced rapidly to powder, while the woody and fibrous parts together with the tracheids and vessels are quite difficult to pulverize. Accordingly, frequent sifting should be resorted to during the process, so that as the broken fragments are reduced to the proper size to pass through the sieve they may be removed. The process of grinding and sifting must be continued until all the tissues have passed through the sieve. Powders in small quantities may be made by means of a mortar and pestle, and if the material is thoroughly dry the time and labor need not be great. A mortar and pestle made rough by the use of coarse carborundum powder has proved very efficient. Coarse powders in considerable quantity may be made in an ordinary small coffee mill. The process of grinding may then be continued by means of mortar and pestle and the fineness carried to any degree desired.
Color.—Vegetable powders are liable to vary greatly in color. Some of the common factors which cause this variation are light, moisture and increasing fineness. Exposure to light deadens the color, in some cases very rapidly, a light or reddish-brown soon becoming a dark or dull brown, etc. By exposure to moisture most powders grow dark in color. Increasing fineness produces varying tints and, in some instances, the quality of the color is wholly changed; for example, Spanish Licorice, in coarse powder, is yellow showing considerable portions of brown cork, while a very fine powder is almost lemon color. If the process be carried on by alternate grinding and sifting, as described above, tints from yellow to light lemon yellow will be obtained. The aging of powders, even when not exposed to light, changes them to darker tints. Powders made from plant parts, rich in oil, are likely to be dark in color and the darkening may become marked if heating is allowed to occur during the grinding. They darken rapidly on exposure to light and are likely to become rancid.
Various systems of classification by colors have been worked out for the vegetable drugs. Doctor Schneider has divided them into six groups as follows: 1, Very light; 2, Yellow; 3, green; 4, gray; 5, brown; 6, very dark. Professor Henry Kraemer forms them into five main groups: 1, Greenish powders; 2, yellowish powders; 3, brownish powders; 4, reddish powders; 5, whitish powders. These groups are subdivided according to the forms of cells, nature of the cell wall and cell products. All such systems as these are more or less artificial, and although useful in many cases, have not proved wholly satisfactory in the laboratory.
Identification by Odor.—The odors from drugs are exceedingly difficult to describe, largely because we have no odor standards at command for comparing them qualitatively or quantitatively. We can understand such terms as aromatic, pungent, fragrant, agreeable, disagreeable, etc. These terms serve in a measure to indicate odor qualities.
The student is recommended to acquaint himself with such aromatic odors as cinnamon, cloves, nutmeg; with the mint family odors, such as peppermint, spearmint, pennyroyal, etc. He should acquaint himself with such odors as are furnished-by the odorous fruits, of the Umbelliferae, such as caraway, fennel, etc.; with camphoraceous odors, as eucalyptus, rosemary, and camphor; with pronounced and characteristic odors of wintergreen, sassafras, etc.; with the delicate and fragrant odors derived from the lemon, orange, orange flowers, etc. He should not omit the study of the disagreeable odors, as we find in conium, valerian, stramonium, garlic, civet, castor fiber, etc. All such odors serve as a means of comparison.
It will be seen that in order to describe an odor it becomes necessary to have some prominent characteristic odor with which to compare. The Pharmacopoeia (viii) states that conium has a mouse-like odor; sumbul, a musk-like odor; lactucarium, a heavy odor; senna is described as having a tea-like odor, etc. Tarry substances that have a creosote or smoky odor are said to have an "empyreumatic odor."
Identification by Taste.—What has been said of the odor of drugs applies also to their taste. Taste is not a very distinctive property. There are some drugs that have a distinctive taste, such as gentian root, which has a simple bitter taste; senega, an acrid taste; ginger, a pungent; geranium, astringent; elm bark, mucilaginous, etc. Many drugs have what may be termed a mixed taste. Hence we find in descriptions such terms as: bitter-astringent applied to cinchona; bitter-pungent applied to orris root; pungent-astringent applied to cotton-root bark; bitter-sweet, applied to dulcamara; sweetish-bitter-pungent, applied to spigelia, etc. Many drugs are tasteless, such as lycopodium, kamala, physostigma, etc.
It is plain to be seen from the foregoing that the taste, as well as the color and odor of powders, is not distinctive enough to identify them with certainty; still, these physical properties serve in many cases as a valuable aid in their identification.
Adulterants and Their Identification.—As stated above, adulteration of drugs is made easier and the detection of adulterants is more difficult when the drugs are reduced to powders. Great skill is required in the identification of adulterants; for the art of drug adulteration is an old one and the materials employed-have been selected, often ingeniously, on account of their very close resemblance to the true articles they replace. In the case of whitish powders, foreign starches, especially the common cereal starches, have been used, and not infrequently have the "scrapings" from bakeries been parched or browned to the proper degree and employed in drug and food adulteration. The endocarp of the olive, cocoanut, and walnuts; exhausted coffees; cocoa shells; and other similar substances, which are composed chiefly of stone cells, have been employed to a large extent in admixture with brownish powders. The use of wheat bran or middlings in ginger has been a common practice. Sometimes inorganic substances such as talc, chalk, clay, sand, etc., are employed. One of the most difficult means of adulteration to detect is the use of exhausted powders (the dregs left from drugs extracted by percolation). These are first dried and repowdered and mixed in various proportions with the pure article. Deteriorated drugs have been used in the same way. It goes without saying that these latter forms of adulteration can not readily be detected microscopically, but a microscopical examination in connection with careful chemical tests is of the greatest value.
A thorough knowledge of the histology of the plant part supposed to constitute the powder is necessary. And for this purpose cross and longitudinal sections, which may be prepared after soaking the dried drug materials in water, may, in many cases, be used to great advantage. By careful comparisons of sections and broken fragments, and the employment of proper reagents upon cell-products, identification is made positive. For a full account of cell-products and reagents, see Part IV, Chapters II and III.
Mounting Powders for Examination.—Powders for microscopical examination should be thoroughly mixed, so that the large and small particles will be uniformly distributed throughout the entire specimen, as before stated. In powders that have been standing for a considerable time the larger particles will be separated from the finer, so that great difficulty may be encountered in obtaining a typical mount from such a powder, unless it has been thoroughly mixed. Only a small portion of powder should be used in making a mount, the amount depending upon the size of the cover-slip to be used. When the mount is ready for examination, the particles should be spread out evenly and should not come in contact one with another so that the large ones might obscure the smaller.
Powders for examination may be mounted directly on the slide, using the proper medium, or the powder may be mixed with the mounting medium in a small test-tube, specimen tube, or homeopathic vial. If a small portion of powder be transferred to a slide, a drop of the desired mounting medium added, and the whole thoroughly mixed and covered with a coverslip, it will furnish a mount ready for examination. However, it is frequently desirable or even necessary to use some clearing agent in order to render dark colored or opaque powders transparent. In such cases the powder should be thoroughly mixed with the reagent and left standing for twelve hours or more, when a portion may be taken up with a pipette and a drop of the mixture transferred to a slide.
Clearing Agents and Mounting Media.—For making temporary mounts of powders water is the best general medium, and should be used whenever a clearing agent is not required. In this medium delicate markings are clearly brought out, and it is especially recommended for the examination of starches. Frequently specimens are filled with air, which must be removed before a satisfactory examination can be made. For driving out air 70 per cent. or stronger alcohol should be used, but this is not a desirable medium for general use, as it evaporates rapidly and allows the specimens to dry up. However, this medium is excellent for bringing out details of structure, and may be profitably employed when a hasty examination is to be made. It can be replaced by water or other media as desired.
Equal parts of water and glycerine furnish one of the best and most useful mounting media. This mixture is especially desirable when delicate markings are not brought out in water. It acts as a clearing agent, and although the action is somewhat slow, it will render most specimens clear enough for examination. Equal parts of water, glycerine, and alcohol make a reagent to be preferred to the above in many respects, and is the most useful of the simple and cheap reagents. This mixture penetrates tissues well, acts as a clearing agent, and does not dry up. Specimens may be kept in it for days or even weeks.
In the examination of many specimens it is necessary to use a strong clearing agent, and it is frequently desirable to have one that acts rapidly. Chloral hydrate, made by dissolving five parts of chloral hydrate crystals in two parts of water, is one of the most common and useful clearing agents. Its action is rapid, but it is not a good medium for mounting in many cases, since delicate markings are not clearly brought out by it. In many specimens starch is dissolved by this reagent, and it should never be used when accurate measurements of starch grains are to be made. However, chloral-hydrate solution with iodine added is the best and most reliable agent for the detection of starch, and is especially recommended where starch occurs in small quantities or is likely to be obscured, as in chloroplasts or by proteid substances.
A clearing agent to be preferred to the above for general purposes may be made by mixing 1 part of 95 per cent. alcohol, 1 part glycerine, 1 part water, and 4 parts saturated aqueous solution of chloral hydrate. This mixture gives a reagent fairly rapid in action, and also serves well as a mounting medium. It is the most useful clearing agent and can be employed in more cases than any other.
Potassium hydrate in 2 to 10 per cent. aqueous solution is valuable as a clearing agent, and also serves well as a macerating agent. It is rapid in action, and dissolves starch. Acetic acid, 20 per cent., and hydrochloric acid, 10 to 20 per cent., may be found exceedingly useful as clearing agents in many cases. They are often valuable in removing starch from specimens where it may interfere in an examination.
In the preparation of specimens which are exceedingly difficult to clear, or in handling coarse powders where the fragments are so large that they must be broken up by macerating before mounting, javelle water and Schultz's macerating fluid will be found useful.
The action of any of the clearing agents mentioned above may be hastened or increased by the application of heat. By holding a mounted specimen over the flame of an alcohol lamp or a Bunsen burner it can be heated without injury, even to boiling, if proper care be exercised.
Measurements.—The fragments of powders should be carefully measured, and the measurements used for comparison wherever it is possible to do so. Measurements should be made with an eye-piece micrometer. In preparing specimens for measurement the greatest care should be exercised in the use of reagents so that objects may not be swollen abnormally or distorted before measurements are made.
On the following pages are given a few examples to show the diagnostic characteristics of some powders which frequently, either by mistake or intentionally, are substituted one for the other.
The first example is illustrated by the barks taken from the same genus —Frangula, Fig. 275, and Cascara sagrada, Fig. 276. A comparison of the fragments composing these two powders shows them to be very similar in structure. Cascara presents one striking difference, as shown by the sclerenchymatous cells, sc, Fig. 276, which occur quite commonly, but occur rarely, if ever, in Frangula. In each of the specimens are bast fibers, but in Frangula the fibers have thicker walls and contain more numerous and well-defined pits than do the fibers of Cascara. Also the cork cells and the large parenchyma cells of the cortex show characteristics which are of diagnostic value. In Frangula the cork cells contain a deep red or purplish coloring substance, while those of Cascara have a reddish-brown coloring substance.
In the large parenchyma cells of Cascara is found a substance yellowish in color which changes to orange upon the addition of potassium-hydrate solution, while in Frangula the large parenchyma cells contain a coloring substance of a much brighter yellow, which upon the addition of potassium-hydrate solution changes to a red or deep purplish color.
The second example is illustrated by two roots taken from closely related species—Brazilian Ipecac, Fig. 277; Psychotria Ipecacuanha (Stokes) of the British Pharmacopoeia; Cephaelis Ipecacuanha (A. Richard) of the U.S.P.; and undulated Ipecac (Fig. 278), which represents species from several different genera, such as Richardsonia, Psychotria, Ionidium, etc. The starch grains from each specimen are similar in form and structure, the only difference being that the starch grains from Brazilian Ipecac, ranging in size from 4 to 15 microns, are uniformly smaller than are those of undulated Ipecac. The elements of the xylem, however, furnish a ready and reliable means of distinguishing between these two powders. The xylem of Brazilian Ipecac consists of tracheids, tra, Fig. 277; and of peculiar strongly pitted wood parenchyma, which somewhat resembles tracheids, fl, Fig. 277. Undulated Ipecac shows the presence of strongly pitted water tubes (pitted vessels), v, Fig. 278, and quite typical wood fibers, fl, Fig. 278. Brazilian Ipecac does not show water tubes, unless fragments of the stems become mixed with the roots.
As a third example, the leaves of Belladonna, Fig. 279, and Hyoscyamus, Fig. 280, furnish an excellent illustration. The epidermal cells of Belladonna are large with wavy walls and the cuticle is striated, es, Fig. 279; while Hyoscyamus has epidermal cells similar in every respect excepting the striated cuticle, ei and es, Fig. 280. The spongy parenchyma of Hyoscyamus contains numerous crystals of calcium oxalate, usually in the form of prisms, cr, ccr, Fig. 280, while Belladonna is without calcium oxalate excepting for crystal sand, which is contained in a few large cells of spongy parenchyma adjoining the palisade parenchyma—c, cr, Fig. 279. The presence of prismatic crystals in Hyoscyamus is the most striking diagnostic character of these two powders.
The trichomes furnish other valuable diagnostic characters, but they are not always reliable, since Belladonna leaves that are almost glabrous, and consequently almost devoid of trichomes, are sometimes found. Either specimen may contain both simple and glandular hairs. The simple hairs are conical and may be composed of one or more cells. In Hyoscyamus the glandular heads, which may be either bicellular or multicellular, pg, Fig. 280, are borne on a stalk composed of two or more cells. The glandular hairs of Belladonna are found with heads either unicellular or multicellular. The larger multicellular glands are usually borne on a stalk consisting of one or two cells, pg, Fig. 279, while the smaller ones are likely to have a stalk composed of several superimposed cells. The unicellular glands are rounded in form and are borne on stalks of several Cells, pg, Fig. 279.
It should be stated that each drug has its own peculiar microscopical elements. Some of these, it is easy to see, are of special value in the identification of drug powders.
As a general direction for the detection of adulteration or admixture it cannot be too strongly emphasized, that authentic samples of the pure drug, and of the suspected adulterant or admixture, should be carefully studied, macroscopically, and microscopically, as a preliminary process. This laboratory method supersedes all the aids in the form of representation by drawings and figures on paper.
An examination of a drug powder should never be considered complete until the sample, has been compared with authentic specimens of the same drug or drugs of the same degree of fineness.
FIG. 281.—Shows Starch-granules of Ipecac. (X 750.) The cells of the bark are filled with starch. The granules are spherical, oblong, or angular, and vary much in size. The hilum is located near the center, and is often seen to be fissured. The grains are smooth, and show no concentric markings. They are often in groups of two, three, and sometimes even more grains joined together.
FIG. 282.—Shows Starch-granules of Jalap. (X 250.) The grains are very numerous in the cells; are large and have characteristic markings. They are rounded or broadly ovate, having the hilum located near the small end and surrounded by excentric lines.
FIG. 283.—Shows the Starch-grains of Veratrum viride (X 350), which so closely resemble those of Veratrum album that it would be impossible to distinguish the two by their starch-grains. Those of the former are often found in groups of twos, threes, fours, and sometimes even more. They are small, rounded, or angular, with the hilum in the center.
FIG. 284.—Represents Starch as it appears in Calumba. (X 350.) The grains are large, and in shape they are circular or oval. A few double or compound grains are found, but they do not occur frequently. The hilum is rather excentric, and is often seen to be fissured in a radial direction. The grains are smooth, and occasionally a curved line or two is to be found.
FIG. 285—Shows Starch-grains as they appear in Galangal. (X 350.) The grains are large and mostly long ovate, but sometimes they are irregular. The hilum is located near the larger end, and is sometimes fissured. The stratification lines are plainly seen on the larger grains and but faintly, if at all, on the smaller ones.
FIG. 286.—Illustrates Starch-grains as seen in a specimen of Iris florentina. (X 500.) These grains are quite characteristic and very abundant. They are rather elongated, rounded or truncate at one end, and usually tapering toward the other end. Occasionally a three-lobed grain is seen. As a rule, the grains are irregular in shape. The hilum is located near the large end, and is slightly fissured. (a) is the most common form. A very prominent characteristic is a double line branching from the hilum and extending toward the other end.
FIG. 287.—Shows Starch-grains as they appear in Caulophyllum. (X 250.) The grains are small, but quite characteristic. They are mostly gathered together in large and roundish masses, consisting of twenty-five to fifty grains. The single grains are globular, or more commonly many-sided, and without hilum or stratification lines.
FIG. 288.—Shows the Grains as they appear in Aconitum napellus. (X 850.) This drug is very rich in starch. The starch-grains are rather large. There are a great many compound grains composed of from two to eight granules. The single grains are round, long, and in some cases have flat faces. The hilum is located centrally, and is seen at times to be fissured slightly. The concentric markings are not discernible.
FIG. 289.—Shows Starch-grains as they appear in Geranium. (X 1200). There are specimens of Geranium in the market that contain little or no starch. This somewhat singular fact is said to be due to the season in which it is gathered. The drug usually contains starch in abundance. The grains are rather long, and appear to be thicker at one end than at the other. The hilum is located generally at the larger end, but sometimes central, and it occasionally appears at the smaller end. The stratification lines are very faintly seen at times.
FIG. 290.—Shows Starch-grains as they appear in Honduras Sarsaparilla. (X 500.) Many of the grains are seen to occur in groups of two, three, and sometimes four. The single grains are spherical or angular, with a hilum located near the center. The hilum in the larger grains is angular fissured. No concentric markings can be seen.
FIG. 291.—Shows Starch as it appears in Podophyllum. (X 550.) The grains are small and mostly single, but sometimes they are double or triple. They are spherical with a central hilum, and are seldom fissured. The hilum can hardly be seen in the smaller grains.
FIG. 292.—Shows Starch as it appears in the rhizome of Hydrastis. (X 1300.) The starch is very abundant. The grains are most commonly joined together in groups of from two to six. The grains, when single, are rounded in form. The hilum is indistinct and unfissured.
NOTE.—The drawings of the starches were made from authentic specimens of the crude drug of the market.
Types of Drug Powders
The following pages <512-519> are illustrations of some of the more important drug powders of the National Formulary and of the Pharmacopoeia, designed to illustrate how characteristic elements may be selected for purposes of microscopical identification.
On pages <520-528> will be found condensed descriptions of the characteristic elements of some of the more important drug powders selected mainly to give as wide a range as possible for purposes of identification.
A Manual of Organic Materia Medica and Pharmacognosy, 1917, was written by Lucius E. Sayre, B.S. Ph. M.