Mounting Microfossils ~ Forams and Glue, Art and Polymaths

In which the blogger exudes enthusiasm for mounting microfossils on slides, and finds, amid the shells and glue, art and polymaths (though he stretches the definition of the latter).

Science and Art

It’s a marriage of science and art.  Mounting the tests or shells of microorganisms on microscope slides is an integral part of safeguarding, organizing, cataloguing, and researching these tiny specimens (generally on the order of half a millimeter or smaller).  But there’s an aesthetic appeal for me in this as well.  Pictured below is a slide on which I’m beginning to categorize some of the foraminifera fossil shells that I’ve found in a sample of Jurassic material (Oxford Clay from Yaxley, England).

Given the gaping holes in my knowledge of these single-celled protozoa and the shells they create, I’m really not sure whether the groups I’m creating are species specific to any degree, or whether I’m simply discriminating among specimens of the same species on the basis of irrelevant physical characteristics or vague traces of the preservation process.  Despite how inchoate this is, I find even this slide to be visually intriguing.

As slides accommodate more and more specimens, their visual appeal can grow markedly.  Case in point – the two slides shown below, prepared by Karl-Otto Bock, contain many shells of recent (not fossils) foraminifera from two locations – a beach at Malia, Crete, Greece (first, very crowded picture) and the ocean floor in the Hebridian Slope in the North Atlantic (second, sparser picture).

(The images of both slides were downloaded from Michael Hesemann’s website of the Foraminifera.eu-Project, and are reproduced under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 Germany License.  The Foraminifera.eu-Project represents the work of scientific amateurs and professionals dedicated to promoting knowledge of, and research about, foraminifera – a rich and very useful site.)

Bock has grouped the foram shells by species on these slides.  How the specimens are arranged within each cell, how many to place in a cell, which species are placed near to each other, where the species with the most bizarre structures are settled, are among the many choices to be made in this process.  Even if Bock gave no thought to the aesthetic effect of the arrangements he’s creating, surely there is one.  And the opportunity for a touch of humor is there – notice the #10 cell in the Crete slide (the first slide) with a foram placed in the 0.  (On the website, clicking on individual cells in a slide brings up information about that species.  Very cool.)

This is painstaking work.  Manipulating the small shells with the fine hairs of a wet brush and positioning and affixing them just so demands a steady hand and an inordinate amount of patience.  There’s luck involved as well given the propensity of the specimens to “jump” if touched with a brush that’s not wet enough.  If one of these escapees manages to end up off the slide and out of the tray in which the slide might be resting, good luck finding it again.

Occupying a special place among mounters of microfossils are Arthur Earland (1866 – 1958) and Edward Heron-Allen (1861 – 1943).  Though amateurs in a strict sense of that term, both men were leading figures for three decades in the study of foraminifera, collaborating on many significant studies.  Among their notable efforts is the study of the foraminifera brought back from Robert Falcon Scott’s star-crossed expedition to Antarctica (1910 – 1912) (Protozoa, Part II.  Foraminifera, British Museum, Volume VI, No. 2, 1922).

Earland, who spent his working life in the Post Office Savings Bank Department, was a “Civil Servant who worked at Forams as a relief from the monotony of his job.”  This is Earland’s own description of himself, if I correctly read his obituary in the Journal of the Royal Microscopical Society, September – November, 1957.  In 1954, he informally estimated that the new foram taxa identified by the Earland/Heron-Allen collaboration included at least 2 families, 1 sub-family, 19 genera, 133 species, and 64 varieties.  The Royal Microscopical Society obituary concludes, "He leaves . . . the reputation of a forthright man of sterling character, the last of the nineteenth century masters of the Foraminifera in Britain."  Perhaps it’s only appropriate that there’s precious little biographical information on the web about this most self-effacing man.

Human Polymath

In contrast, Heron-Allen continues to captivate nearly 70 years after his death.  (The brief portrait of Heron-Allen which follows is based largely on information in R.B. Russell's Short Biography of Edward Heron-Allen appearing on the Heron-Allen Society website, and Edward Heron-Allen:  the Man and his Scientific Library, by Clive Jones which was published in the Winter 2004 issue of Set in Stone, the newsletter of the Palaeontology Department of the Natural History Museum, London.)

Russell asserts that, despite the man's many diverse areas of endeavor, “[r]ather than a dilettante, Heron-Allen is better described as a polymath.”  Heron-Allen trained and worked, at times, as a lawyer, but that was the least of it.  His scientific work, including his collaborations with Earland, was so highly regarded that he was elected in 1919 to the Royal Society.  He also apprenticed himself to one of the period’s foremost violin makers, made violins, and wrote extensively on them.  Among his books was the popular Violin-Making:  As It Was and Is (1914).  He also studied languages, publishing several translations of Persian literary works, including one of The Rubaiyat of Omar Kahyyam.  In the 1880s, Heron-Allen dedicated himself to palmistry or cheirosophy (also spelled chiromancy).  On this, too, he published successfully and then undertook a triumphal tour of the United States.

He turned to fiction; among his novels was a light romantic novel which he titled The Romance of a Quiet Watering-Place (Being the Unpremeditated Confessions of a not altogether frivolous Girl) and published in 1888 under the pseudonym Nora Helen Warddel (an anagram of his name).  Later, as Christopher Blayre, he wrote tales of the supernatural, such as The Purple Sapphire.

I would note that, perhaps for good reason, The Purple Sapphire, which is tale of a cursed gem stone purloined from a Hindu statue during the Indian mutiny in the 1850s, has the ring of truth to it.  The website of the Natural History Museum describes (7th slide at this link) a purple sapphire in its collection, and on display in its “vault,” as having been looted during the Indian mutiny and associated with misfortune for all of its owners since.  According to NHM, the sapphire’s final owner, Edward Heron-Allen, deemed it cursed and locked it away in an bank.  After his death, his daughter gave it to the NHM.  An appropriate dénouement, given that in the short story, the stone’s final resting place is the museum at the fictitious University of Cosmopoli.

One special aspect of the Earland and Heron-Allen collaboration was their Christmas slides.  Giles Miller, the NHM Curator of Micropalaeontology, describes in a post (Microfossil Christmas Cards) on his always fascinating blog that, at Christmastime, Earland and Heron-Allen exchanged microscope slides on which they had mounted foraminifera fossils.  The practice continued until the early 1930s when their friendship ended.  Pictured below is a slide from Christmas, 1912.

Simply amazing.  Clearly written in forams is “AE XMAS 1912.”  When I first saw the photograph of this slide, I was stunned first by the startling realization that these men had beautiful fossil foram tests in such abundance that they could indulge in this activity, and then by the time and patience required to render this piece of art.

Not shown in the photograph are the handwritten notes on the slide:  “Xmas 1912” and “Prosit!  AE.”  (They can been seen at this link at the NHM.)  I believe this particular slide was a gift from Earland to Heron-Allen.  The picture is copyrighted by The Natural History Museum, London, and is used with permission.

Botanical Polymath

But Heron-Allen isn’t the only polymath I have stumbled upon as I pursue my interest in mounting microfossils on slides.   I have found what I can only term a botanical polymath - gum tragacanth.  The adhesive I use to affix microfossils to slides is a solution of water and gum tragacanth.  When I began to work with microfossils on my own, I followed the lead of paleobiologists Howard Armstrong and Martin Brasier who, in their Microfossils (2nd edition, 2005) advise,

Adhesion of microfossils is improved by brushing the slide’s surface beforehand with a weak solution of Gum Tragacanth to which a drop of Clove Oil has been added (to reduce fungal growth).  (p. 279)

When the gum tragacanth solution dries on the slide, it is ready to receive individual microfossils.  Transferring a fossil to the slide with a slightly wet brush activates the water-soluble glue which will hold the fossil in place when it dries.  Of course, being water-soluble, the glue easily releases the microfossil when moistened.  Whether the clove oil will actually retard fungal growth remains to be seen, but there’s a delightful scent released as my wet brush touches the dried solution.

Over the years, many different adhesives have been suggested for microfossils, but the gum tragacanth solution appears to have remained among the favorites, cited often in books and articles describing working with microscopes to view microorganisms.  For instance, in 1922, Arthur Earland wrote

The best fixative for mounting is gum tragacanth, which is almost invisible when dry, being quite devoid of the objectionable glaze which characterizes gum arabic.  It is also much less subject to variations of moisture than gum arabic which alternately contracts and expands with changes of weather and often fractures delicate forms.  Powdered gum tragacanth should be used in the preparation of mucilage.  (Collecting and Preparing Foraminifera, in Modern Microscopy:  A Handbook for Beginners and Students, edited by M.I. Cross et. al., p. 263.)

Still earlier, in 1859, William Lowndes Notcutt recommended that opaque objects, which required the focusing of an external light source, be mounted on blackened slides with “mucilage of tragacanth, also previously mixed with black.”  (A Handbook of the Microscope and Microscopic Objects, p. 28)

Gum tragacanth is the dried sap from Astragalus gummifer, a plant known by various common names such as goat’s-thorn and tragacanth milk-vetch.  The plant is a small, thorny, evergreen shrub, native to the semiarid grasslands and dry mountainous areas of Western Asia, including Iran, Lebanon, Syria, and Turkey.

This illustration is taken from Medicinal Plants, Being Descriptions With Original Figures of the Principal Plants Employed in Medicine and An Account of the Characters, Properties, and Uses of Their Parts and Products of Medicinal Value, by Robert Bentley and Henry Trimen, Volume II, 1880, entry 73.

Gum tragacanth has a extensive history, having been described, according to biochemist Amos Nussinovitch, at least as early as 300 years before the beginning of the Common Era.  (Plant Gum Exudates of the World, 2009, p. 55.)  It has long been part of Materia Medica, the study of pharmaceutical chemistry, particularly those substances derived from plants.

Bentley and Trimen describe how the gum naturally emanates from breaks in the plant’s stem, in a flow likened by one authority they cite to a “worm.”  The harvesting of quality gum tragacanth involves digging around the base of the stem, making an incision, and collecting and drying the gum that streams from that cut.  If properly prepared, the material collected from these incisions dries in white flakes.

Chemically, the gum is an edible, complex, acidic polysaccharide.  Agricultural biochemist Mark Dreher explains that

Tragacanth is composed of a mixture of polysaccharides:  traganthic acid, a water-insoluble component, which confers water-swelling properties to the gum; and arabinogalactan, a water-soluble polymer that gives the gum solubility.  (Food Sources and Uses of Dietary Fiber in Complex Carbohydrates, edited by Susan Sungsoo Cho, et al., 1999, p. 347.)

In solution, it is very viscous or gel-like.

Gum tragacanth has been exploited for centuries for its thickening, binding, water absorbing, and stabilizing attributes.  It is incredibly versatile; I learn of new uses in nearly every additional source I consult.  At the same time, the volatility of the part of the world from which it originates, has led to the search for alternatives.  (I must also admit that I don't know if other plant gums, such as gum arabic, are equally versatile.)

Here, then, are just some of the applications of gum tragacanth.  It has been added to many, many foods, including salad dressings, sauces and gravies, ice cream, sherbet, chocolate milk, processed cheese and cheese spread, syrups, catsup, and candy, particularly chewy candies.

[Later edit:  With the passing of superstorm Sandy along the east coast of the U.S., I was finally able to wander the aisles of my local grocery store and gauge the extent to which alternatives have displaced gum tragacanth in foods.  Apparently, it's been a thorough overthrow.  I discovered no mention of gum tragacanth for foods in which it might have been used in the past.  Xanthan gum appears fairly frequently, a gum that offers a fascinating story on its own, being the byproduct of a fermentation process involving certain strains of bacteria.]

Beyond food, gum tragacanth has been used as a laboratory culture medium; a digestive tract stimulant, treating both diarrhea and constipation; a treatment for tumors; burn dressings; a thickener for textile dyes, ink, water colors; a binder in paper manufacture; and, of course, glue (including the sealer for the final, outermost leaf in cigars).  It is also added to toothpaste, lotions, denture paste, and spermicidal jellies.  Given the last application, it’s probably appropriate that, for millennia, it has also been considered an aphrodisiac.

I must mention one final use of gum tragacanth.  Edward Heron-Allen noted, in Violin-Making:  As It Was And Is, that the gum has been an ingredient in the varnish applied to violins.

Interesting where forams and glue may take you.


Sources Used But Not Specifically Cited in This Post

David Julian McClements, Food Emulsions:  Principles, Practices, and Techniques, 2004.

Rebecca Johnson and Steven Foster, National Geographic Desk Reference to Nature’s Medicine, 2008.

Entry for Astragalus gummifer on the website of Plants For A Future.

Entry for A. gummifer on the Ecocrop website of the UN’s Food and Agriculture Organization.

Entry for A. gummifer on the U.S. Department of Agriculture’s Germplasm Resources Information Network website.

Entry for tragacanth on the WebMD website.