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Craving EarthUnderstanding Pica--the Urge to Eat Clay, Starch, Ice, and Chalk$

Sera Young

Print publication date: 2012

Print ISBN-13: 9780231146098

Published to Columbia Scholarship Online: November 2015

DOI: 10.7312/columbia/9780231146098.001.0001

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Medicine You Can Walk On

Medicine You Can Walk On

(p.32) Chapter Three Medicine You Can Walk On
Craving Earth

Sera L. Young

Columbia University Press

Abstract and Keywords

This chapter describes the many ways that pica substances have been used to heal a range of ailments. It begins by discussing some of the physical and chemical features of clay. It then describes clay known as terra sigillata, which was valued by the ancient Greeks and Romans for its healing properties. Pliny, for instance, wrote about how terra sigillata could be used as an antidote to swallowed poisons and snakebites, as a treatment for dysentery, and to reduce inflammation around the eyes. The remainder of the chapter covers the history of clay in Chinese pharmacopeia and how but earth continues to be used by modern medicine as effective treatments for diarrhoea and wound healing.

Keywords:   pica substances, geophagy, medicine, terra sigillata, diarrhoea, wound healing, medicinal properties, clay, Chinese pharmacopeia

NOT ALL GEOPHAGY is pica. Inadvertently swallowing a clod of dirt in your freshly picked arugula or politely smacking your lips on your son’s mud pie are indeed geophagy, but pica are they not. You’ll recall from chapter 1 that one component of the definition of pica is that it involves strong cravings. Thus, because neither of these instances includes a desire for earth, they would not be considered pica, although they are both geophagy.

This chapter is about non-pica geophagy in the field of medicine. How is that germane to a book about pica? Most importantly, understanding the healing powers with which pica substances have long been imbued provides clues to the function of pica. As an added bonus, some fascinating details about the role of religion and science in mundane modern pharmaceuticals are unveiled. Because all earths used in medicine are clay-rich, I shall begin by discussing a few of the physical and chemical features of clay.

The Amazing Properties of Clays

Although they may seem lackluster, clays are actually capable of dynamic and astounding feats. They are also very complex; many scientists have (p.33) dedicated their entire lives to their study. What follows is a cursory introduction to what clays are and how they interact with their environments. Both pieces of information are critical for discussions throughout the rest of the book.

What Is a Clay?

Soil is made up of both organic and inorganic constituents. The part where most microbial activity happens is in the humus, the rich, dark brown stuff mostly made of decayed organic matter. (You’ll recall from chapter 1 that geophagists stay away from humus-rich soil.) The inorganic components are essentially the product of the parent rock(s) from which the soil derives. They may closely resemble the boulder from which they eroded, or they may be greatly altered by weathering, which causes the rock to decompose into various particle sizes. In descending size order, these are medium to coarse sand (0.2–2 mm), fine sand (0.02–0.20 mm), silt (0.002–0.02 mm, still visible to the naked eye), and clay (<0.002 mm, impossible to see an individual particle). Here’s an indication of the magnitude of size differences. If you drop a particle of course sand in water, it will fall about 10 cm in 1 second. A particle of silt will fall 10 cm in about 5 minutes. A particle of clay will take 860 years to fall the same 10 cm (Logan 1995:116). As we shall see, this very small particle size makes clays extremely useful in a range of applications.

There are several types of clay minerals (Loveland et al. 1989; Millot 1979: see also table 3.1). Scientists use the term clay minerals to refer to groups of clays with similar layer structures. Clay minerals are all phyllosilicates, a category of silicate minerals made up of parallel sheets, usually of an aluminosilicate (“phyllo” means sheet). The term clay is used to refer to materials that consist largely of different sorts of clay minerals (Millot 1979).

Clays, the smallest particles in rocks, are fascinating for many reasons, including their physical structure. If you look at granite, say, on a fancy kitchen countertop, you can easily see its crystalline structure. Clays, too, have similar crystalline structures, only theirs are microscopic (Millot 1979). Geochemist Dr. Lynda Williams, whose work on medicinal clays is discussed at the end of this chapter, describes clay crystal structures by way of an analogy to a peanut butter and jelly sandwich (Coulombe 2007). The slices of bread in the clay structure are extremely thin layers of flat aluminosilicate sheets that are negatively charged. These negative surfaces (p.34)

Table 3.1 Characteristics of the Clay Mineral Groups

Clay Mineral Group

Example of Clay

CEC* (mEq/100g)





Kaolinite, halloysite


Palygorskite (formerly known as attapulgite)

Fuller’s earth


Smectite formerly known as montmorillonite)

Montmorillonite, saponite


(*) Cation exchange capacity

Note: Adapted from (Loveland et al. 1989; Millot 1979).

attract positively charged atoms, called cations. Examples of cations include Fe3+, Fe2+, Mg2+, and K+. Cations may be thought of as the peanut butter on the bread. Continuing the analogy, the jelly is composed of organic compounds that are also sometimes adsorbed1 between the silicate layers.

Clays have the ability to adsorb a wide variety of molecules, especially when they are dispersed in water. A measure of how readily a substance can exchange adsorbed cations—those positively charged molecules stuck to the “bread”—with cations in a surrounding solution is called the cation exchange capacity (CEC). If the cation exchange capacity is low, a clay mineral is less likely to form an insoluble complex with cations. If the cation exchange capacity is high, cations are likely to become bound tightly to the substance and thus be unavailable to be metabolized. Cation exchange capacity varies enormously, from about 2mEq/100g in kaolinite to approximately 150mEq/100g in some smectites. The likelihood of cation exchange also depends on the strength of charge of the cations in solution. The stronger the charge of the cation already bound to the “bread,” the less likely it will be replaced by another cation. For example, Fe3+ cannot ordinarily be replaced by Fe2+.

In addition to the binding capacity it makes possible, such a crystal structure is also responsible for clays’ high surface-to-volume ratios. There is only a small amount of accessible interior space when the parent minerals are still part of a rock, but as they weather into small clay particles, the surface area greatly increases. For some perspective, one gram of clay can have a surface area larger than a football field (Logan 1995:125).

(p.35) Industrial Uses of Clay

There are many industrial uses of clay, all of which are based on its extraordinary binding capacity. Fuller’s earth, also known as calcium montmorillonite, was used for centuries to absorb lanolin, oils, and other greasy impurities in wools (Robertson 1986). Today, most landfills include a layer of clay to prevent contamination of the groundwater by the sludge that oozes out of our trash. In fact, clay liners are used in all kinds of waste management contraptions, including lagoons and ponds built to contain liquid wastes and berms to contain spills. Clays are used to clean up massive oil spills and to isolate radioactive waste. The clay in kitty litter helps to absorb the pungent smell of Felix’s business. And clays are used to filter vegetable oils, remove heavy metals from wastewater, and purify the air we breathe. Think, too, of the mud masks applied to draw out impurities that would otherwise mar our pretty faces, and the mud baths, considered therapeutic for their beautifying and cleansing powers.2 In short, clays are excellent at removing unwanted molecules.

The small particle size of clays also makes them useful in the paper industry. In fact, they function similarly to starches in paper production (more on this under “Starch” in ch. 9, p. 126). Clays are used to smooth out paper and cardboard by filling in the crevices around the wood pulp. Clays are also used to coat paper, to prevent the bleeding of ink (Millot 1979).

When it is dusted on surfaces, the fine powderiness of clay makes it an effective barrier against insects, too. How? As insects land on clay-dusted surfaces, the clay works its way into the waxy coating of their bodies; it is microscopically abrasive. Eventually, these cuts and scratches cause insects to shrivel and die. It’s a pest-control strategy that is gaining popularity, for there are a number of advantages: it’s not a poison; it doesn’t lose potency over time; and it is not harmful to most larger animals.3 In short, this myriad of uses of clays means you can probably find them in every room of your house, from garage to bathroom.

Early Pharmacopeia

The Rise and Fall of Terra Sigillata

Saltwater taffy–sized hunks of clay from a tiny Greek island were once literally worth their weight in gold (fig. 3.1). This clay was called terra sigillata, which means “stamped earth” (sigillum, Latin for “seal”). The “stamp” refers (p.36)

Medicine You Can Walk On

Figure 3.1 Earliest examples of terra sigillata, when goats were prominent on the seal (Thompson 1914).

to a mark of quality or origin pressed into the clay, much like the signet rings that kings and queens pressed into melted wax to seal their royal missives.4

Terra sigillata was so valuable because of its healing properties, as espoused by the medical literature of the time. Admittedly, in the first century c.e. there was not a wide variety of medical literature to choose from. In the Roman Empire, there was Pliny’s Naturalis Historia (Pliny/Rackham 1952) and in Greece, Dioscorides’ De Materia Medica (Dioscorides et al. 1934); both discussed the medicinal uses of terra sigillata.5 (Appendix A may help you to contextualize the historical events described here.)

Pliny wrote about terra sigillata in several sections: how it could be used as an antidote to swallowed poisons and snakebites, as a treatment for dysentery, and to reduce inflammation around the eyes (Pliny/Rackham 1952). Of terra sigillata, Dioscorides wrote:

But it hath an eminent faculty of antidot against deadly poisons when drank with wine, & being taken before, it constrains to vomit up poisons. It is good also against ye strokes & it is good for ye bitings of venemous poison-outcasting beasts. It is mixed also with Antidotes. And some also use it for expiations. And it is good also for dysenteries.

(Bk. 5, ch. 113)

But what, exactly, was this mysterious terra sigillata? First-century readers could not know for another one hundred years, until 167 c.e., when the great physician Galen visited the Greek island of Lemnos, the source of terra sigallata. His visit was the world’s first eyewitness account of its collection (Tozer 1890).6 He described the solemn production of terra sigillata with great detail:

The priestess collects this, to the accompaniment of some local ceremony, no animals being sacrificed, but wheat and barley being given back to (p.37) the land in exchange. She then takes it to the city, mixes it with water so as to make moist mud, shakes this violently and then allows it to stand. Thereafter she removes first the superficial water, and next the greasy part of the earth below this, leaving only the stony and sandy part at the bottom, which is useless. She now dries the greasy mud until it reaches the consistency of soft wax. Of this she takes small portions and imprints upon them the seal of Artemis, namely the goat, then again she dries these in the shade till they are absolutely free from moisture.

(Cited in Brock 1929:194)

Galen subscribed wholeheartedly to the medicinal properties of these seals; indeed, he took 20,000 tablets with him back to Rome.

Fueled by the praises of these esteemed physicians, the popularity and price of terra sigillata increased over the next centuries until they were “considered equivalent with gold” (Thompson 1914:440). By then, they were used by physicians, healers, and midwives throughout Europe to treat smallpox, dysentery, and pestilential (epidemic-causing) diseases (Forestus/Burri 1982 [1557]; Mérat and de Lens 1834; Salmon 1691). Sometimes it was used by itself and other times as part of a concoction of cryptic ingredients like treacle of Andromicus and Hungary powder. In addition to treating illnesses, it was also used preventatively: royalty swallowed a tablet with their meals as a safeguard against being poisoned (Thorndike 1923). By the end of the sixteenth century, terra sigillata was in such great demand that ambassadors “were accustomed to take supplies of it with them to present to distinguished men” (Thompson 1914:440).

In fact, Lemnian earth had become so desired and so costly that it was frequently counterfeited and “almost every country in Europe strove to find within its boundaries a source of supply of so valuable and profitable a commodity” (Thompson 1914:435). Eventually, other earths did gain repute, including those from Silesia, Poland (called Terra sigillata Strigoniensis), Samos, Greece (Terra sigillata Samia), Sicily (Terra sigillata Sicula), and Jerusalem (Terra sigillata Hierosolymitanae, rhymes with Jerusalemitan) (Mérat and de Lens 1834). And just like in Lemnos, earths from these places had their own special seals (Dannenfeldt 1984). Terra sigillata was soon no longer synonymous with the sealed earth tablets from Lemnos, but rather with a whole variety of earths (Dannenfeldt 1984).

This value and fame incited a multitude of travelers to visit Lemnos.7 Pierre Belon, a French naturalist, was one such visitor and provided one of the most informative accounts of the extraction of the earth for terra sigillata (Belon 1588). His sixteenth-century description reflected the (p.38)

Medicine You Can Walk On

Figure 3.2 Lemnian terra sigillata from the time of Turkish occupation (Belon 1588).

changes in religion, control of natural resources, and political power wrought by the many wars between Turkey and Greece. For example, by the sixteenth century, Hellenic priestesses had been replaced by male Christian priests and monks8 and the digging only happened once a year, before sunrise on August 6. Prior to the removal of earth, Christian priests held a mass in a little chapel that had been built at the foot of the hill. Muslim religious authorities, called khodjas, also participated in the ceremony by sacrificing a lamb. The mass was well attended, with more than 3,000 in the crowd; even the Ottoman governor, who was Muslim, was there.

The priests presided over the collection of earth, and it took fifty or sixty diggers to reach the depth where the holy earth was found; it was no longer the solitary endeavor of a priestess. Up to seven mule loads of earth were taken, most of which was sent to Constantinople, the then capital of the Ottoman empire. Another change since Galen’s visit was that the seal pressed into the clay pieces was no longer a goat; after the Turkish Muslim occupation of Lemnos, this idolatry was replaced with the script tyn mahktoum (Mérat and de Lens 1834), meaning hidden, concealed, and/or secret mud (fig. 3.2).

We know from the English scholar, Henry Tozer, that by 1890, interest in the ceremony was on the decline:

(p.39) [It] is evident from the neglect into which it has lately fallen, that ere long it will be a thing of the past. For several years the Turkish governor has ceased to attend, and, following his example, first the khodjas and then the priests absented themselves, and no lamb is now sacrificed. Last year only twelve persons were present. Though the tablets were to be bought in chemists’ shops in Kastro at the time of Conze’s visit to the island in 1858, I enquired in vain for them; and neither the existing governor, nor any persons of the younger generation, had heard of this remedy. In the eastern parts of Lemnos, however, it is still in use for fevers and some other disorders, for the women possess nuts of it, which they string like the beads of a rosary; these they grate in case of illness, and take a teaspoonful of the powder in water. Not long ago the proprietor of the hillside applied for leave to plough over the spot and sow it with corn; and though for the time this was not allowed by the government, yet, when the annual celebration has come to an end, the prohibition will safely be ignored, and from that time forward the locality itself will be forgotten.

(Tozer 1890:265–66)

Lemnian Earth Today

Is Lemnian terra sigillata still obtainable? To answer this question, esteemed food geographer Professor Louis Grivetti at the University of California, Davis, went to Lemnos on a quest similar to Galen’s. On August 6, 1984, he hired a taxi and driver, Tsokhas, to bring him to Kotsinos (Greek: Kovtsinoı), the alleged site of the holy earth. If Grivetti’s efforts sound quixotic, Tsokhas was, as you’ll see, his Sancho.

After the airport, the road to Kotsinos was rough…. The road worsened and we reached the sea. There is Kotsinos, Tsokhas said—my first view. This view was one of semi-shock; Kotsinos consisted of 3–5 houses, a whitewashed church on a mound (archaeological mound?) and the bronze statue of Morula [heroine of Lemnos]. But where were the pilgrims? Where were the hundreds coming from all over the island to celebrate the Iasus Soteros on August 6th? I expected busloads, cars, carts, people walking, milling about, the air of a traditional feast celebration. There was not a sound—or any activity!

Tsokhas drove into “town” past a taverna and parked. One fisherman was visible on the breakwater; two men were sitting in front of the café. We greeted them, and spoke to the owner, a woman…. Yes, the site (p.40) for digging the clay was nearby along the southwestern hillside (as the guidebooks said)—but each asked why we wanted to go there? No one goes there; no one digs the clay—that was in the time only of the Turkish Sultans. No priest—in their lifetime of memory—had ever blessed the ground; but they used to do so in the time of the Sultans. The priest would go before dawn on one day of the year—not August 6th—and bless the ground, and the clay would “come forth from the ground like toothpaste.” It would be collected, and given to people, especially used by the Turks to test for poison….

With great anticipation we (at least I, for Tsokhas was not looking forward to the next stage) drove to the southwest and parked. We walked through a recently harvested wheat field and hailed a shepherd (and his two dogs) who welcomed us. Yes, the clay site was on the hill, just around the eastern spur, midway up the slope. We should go there, find another person, and ask permission to dig. I was really excited; the link with past and present was flowing and I could sense this wonderful feeling of anticipation.

The total site was covered with thistle, star thorn, and other weeds. Simple digging was all gravel and loose rock! No fine clay sediment! I was very disappointed. Tsokhas, hoe in hand, sat on the vertical rock at the east end. I climbed to the crest of the hill and looked down on the scene. A strange “V” trench snaked below me. The two stones were clearly at the northeast end of a rectangular depression; it looked like a church foundation. Two donkeys grazed beyond the stones; we had not seen them earlier. Below me to the north was Kotsinos, the church, and ugly Morula gazing seaward! Legends and hopes die hard; it was time to leave.

(Grivetti, unpublished fieldnotes)

The poor professor took the disappointment rather hard, as reflected by his poem, “Old Dreams Die Hard,” penned that very day.

  • Old dreams die hard.
  • When truth reveals a different vision of the past,
  • Embellished myth that cannot last,
  • Old dreams die hard.
  • Old dreams die hard.
  • The search for truth is endless and must ever stand,
  • Upsetting theories built on sand,
  • Old dreams die hard.

(p.41) Grivetti’s discovery of a whole lot of nothing in the way of terra sigillata on Lemnos has since been confirmed by a 1992 visit by a Financial Times journalist (Spence 1993) and a visit by a scholar, Rudolph Reinbacher, in 2000 (2002). During Reinbacher’s visit, he did, however, get a sample of clay-based antidiarrheal medicine from his taxi driver’s mother.9 Ironically, the local pharmacist decried it, and recommended a far more expensive preparation: Kaopectate.

Beyond Europe

Europe was not the only place where clay was sought after as medicine. Earth has long had a place in the Chinese pharmacopeia. Ch’en Nan, a Taoist Xian (a person who transcends mortality) born in the early 1200s, had the power of curing diseases with medicine made of earth kneaded with charmed water. Although he was most famous for floating across a river standing on his hat, the healing properties of this medicine earned him the nickname “Mud-pill Ch’en” (Yetts 1919).

The sixteenth-century Chinese physician Li Shizhen listed pharmacological uses for sixty-one clays, muds, and other earths in the most complete and comprehensive medical book on the history of traditional Chinese medicine, Bencao Gangmu. The earths he listed could treat conditions from malnutrition to infection to diarrhea. Unfortunately, many are described too obtusely to identify today, e.g., “soil underneath the shoe,” “soil from the northwest of China.” Healing earth also made its way into a French missionary’s encyclopedic survey of everything Chinese, described as “a certain soft Stone or Mineral, call’d Hiung hoang, of which they make Vessels; and the Physicians esteem it as a sovereign Remedy against all sorts of Poison, malignant Fevers, and contagious Heats in the Dog-Days” (Du Halde 1741:226–27).

In fact, around the world, a number of earths found their way among the cinnabar, frankincense, unicorn horns, and dried newts on physicians’ shelves. In parts of the world that valued the written word, the many recommended uses of earth are well documented. Clays show up in inventories of materia medica in Sumeria (Ebers 1889), India (Chopra 1933; Duttet al. 1980; Jee 1896), the Middle East (Budge 1913; Guiges 1905; Ibn el-Beithar and Leclerc 1877; Mohaghegh 1976), and South America (Cobo and de la Espada 1890).

In places where the written word was less central, proof that earths have been used to treat a variety of maladies comes from reports by outsiders. (p.42) Some were important during fertility and birth. For example, clay was thought to facilitate a quick delivery and expulsion of afterbirth in Mongolia (Pallas 1776), and a handful of fine clay in wine was drunk to avoid a spontaneous abortion in the Canary Islands (de Hoyos Sáinz and de Hoyos Sancho 1947). Most of the documented uses, however, were related to the treatment of gastrointestinal ills. In the Congo, red clay was used to quell diarrhea (Costermans 1895); Australian aborigines (Roth and Etheridge 1897) and Native Americans in the Great Lakes region (Kinietz and Raudot 1965) used clay pills for the same purpose. In the Philippines, clay was used to treat cholera and dysentery (Cole and Gale 1922) and in Siberia, bright yellow chalky earth called stone butter was used to treat cholera (Muller 1722).

Modern Medicine

It may come as a surprise, but earth remains in our modern pharmacopeia, although the snazzy packaging does much to disguise the active ingredients. As described below, it is used both internally and topically.

Clays have been scientifically validated as effective treatments for diarrhea (more on this is chapter 9). In fact, you may have already swigged some clay, albeit in far more industrialized wrapping than old Mud Pill Ch’en offered his ailing clientele. Kaopectate™, the largest-selling over-the-counter medicine for nausea and diarrhea in the United States, gets its name from the original active ingredient—kaolin, one type of clay.10 However, clay is no longer the active ingredient due to formulation changes in the 1990s, and as such, Kaopectate is a misnomer.11

Other clays, however, do remain in current medical use. Smectite (another type of clay) is the active ingredient in a preparation that quells heartburn and diarrhea called Smecta™, and is used quite regularly to treat gastrointestinal problems in Europe, Asia, and Africa.12 Clinical studies on smectite and diarrhea in children have demonstrated that smectite administered with oral rehydration solution (an electrolyte mixture that prevents dehydration) shortens the course of diarrhea by an entire day, compared to just oral rehydration solution by itself (Szajewska et al. 2006).

The second major application of clays in modern medicine is external, for wound healing. This use is also very old. Galen reports that clay promoted the closure of wounds, including the bite of a mad dog; Pliny mentions it as a remedy for ulcers in the humid parts of the body such as the mouth or anus. The popularity of topically administered clays has waxed (p.43) and waned over the centuries, but interest in healing properties of clay resurged in the late nineteenth century in both the United States (thanks to the efforts of a surgeon, Dr. Addinell Hewson), and in Germany (thanks to the efforts of Dr. Julius Stumpf) (Reinbacher 2002).13

Dr. Hewson’s inspiration for the treatment of his patients’ infected wounds with clay was a little-known invention called an Earth Closet, a kind of chamber pot that you “flushed” by dropping earth over your deposit. He reasoned that the deodorizing power of clay made it a likely candidate for disinfecting wounds. Indeed, it seemed to work wonders for his patients. Hewson filled a book, Earth as a Topical Application in Surgery, with 93 case studies and photographs of his successful non-infected amputations (Hewson 1872; see also fig. 3.3).

In Germany, Dr. Stumpf’s attention was called to the desiccating effects of clay when he attended the exhumation of a woman who had died shortly after giving birth. Although she had been buried for more than three years, he was astounded to see that her body was still intact, right down to where the placenta had been attached to the uterine wall. He noticed that the earth in which she had been buried was very clayey; this observation, together with some reading of Pliny and Galen, caused him to hypothesize that clay might resist decomposition because it was inhospitable to bacterial growth.

Shortly after this observation, he was called to treat an old man with rank, putrid bedsores that exposed his tibia in two places. Stumpf decided that an amputation was necessary, but the old man refused. With no other recourse, he dusted what was then known as bolus alba, more commonly known as kaolinite, a fine, powdery white clay, on the sores. The odor was soon gone and the wounds healed shortly thereafter, obviating the amputation. Stumpf proceeded to treat a number of badly infected wounds with this clay. Wounds from infected amputations, dog bites, and gory rifle accidents all healed after bandaging the infected site with clay compresses.

Emboldened by this topical success, Stumpf began to explore the potential for clay to heal internal problems. We can surmise that his conviction about the utility of this treatment was very strong: his first patient was his 81-year-old mother! She was vomiting violently, with severe cramps and diarrhea. He gave her clay with a little water twice an hour, and much to everyone’s amazement, she had recovered by the following morning. After this success, he used clay to treat other patients with severe diarrhea and vomiting, all of whom experienced similar recuperation. When cholera broke out in Germany in 1904, Stumpf was summoned to oversee the treatment of those infected using white clay. His efforts were successful, and for (p.44)

Medicine You Can Walk On

Figure 3.3 Dr. Addinell Hewson’s infection-free handiwork (1872).

this he was decorated by several governments and received 300 free packets of bolus alba from Merck Pharmaceuticals. Another result of his medical successes is that white clay caught on in Germany. Bolus alba began to be used to treat diphtheria, gangrene, and eczema, and to prevent infections of the umbilical cord of newborn babies.

(p.45) Despite these apparent successes, clays have never caught on in mainstream surgical medicine in the United States or Europe.14 Hewson was ridiculed by his American colleagues for using “dirt” in his treatments. And just as Stumpf’s work was gaining momentum, antibiotics were discovered, and these wonder drugs seemed to resolve most patients’ infections.

However, now that we are facing increasing problems with antibiotic resistance, attention is once again being turned to topical uses of clay. Geo-chemist Dr. Lynda Williams and microbiologist Dr. Shelley Haydel at Arizona State University are studying the detoxifying properties of clays from around the world and have discovered that a handful are able to kill bacteria of major public health threats, like methicillin-resistant Staphylococcus infections and Buruli ulcers (a mycobacterium) (Haydel et al. 2008). It seems the scientific community’s interest in the medicinal properties of clay is coming full circle.


(1.) Adsorption and absorption are similar but not synonymous. Adsorption refers to the gathering molecules on a surface (think static cling on a cheap synthetic blouse). Absorption refers to the permeation of molecules (think a sponge saturated in water).

(2.) One beneficiary of the beautifying effects of clay was Cleopatra. She took mud baths regularly, and their beautifying consequences are alleged to have helped her to seduce not one but two of the most powerful men of her time, Julius Caesar and Mark Antony. This, in turn, helped her to achieve influential positions in a succession of Egyptian and Roman governments.

(3.) On a related note, a non-clay but still very finely powdered chalky substance called diatomaceous earth (because it is made of tiny fossilized diatoms) is also useful against insects, including those foot soldiers of urban ickiness, cockroaches.

(4.) Further elaboration on the events described in this section can be found in Dannenfeldt (1984), Hall and Photos-Jones (2008), Hasluck (1909), and Thompson (1914).

(5.) Dioscorides, a Greek physician and pharmacologist (40–90 a.d.), and his Roman contemporary Pliny the Elder, naturalist and military leader (23–79 a.d.), were (p.175) the first to write about the medical properties of terra sigillata. For some context, this was a time when all that was known about medicine, plants, agriculture, architecture, sculpture, geology, and mineralogy could be contained in one place: Pliny’s book Naturalis Historia. Dioscorides was so knowledgeable (or, rather, scientific knowledge was so limited for so long) that his five-volume oeuvre, De Materia Medica, was the basis of most medical practice for 1,600 years (Dioscorides et al. 1934).

(6.) And even then, it nearly did not happen. On Galen’s first attempt, on the way to Rome from Asia, the port at which they docked was on the opposite end of the island from the site of the terra sigillata, and the captain would not wait for the esteemed Galen to collect his specimens. On his second visit to Lemnos, on the way back home to Asia, Galen made sure to arrive at a port near the healing earth (Tozer 1890).

(7.) There are many accounts of such visits, but this is my favorite title: The totall discourse of the rare adventures & painefull peregrinations of long nineteene yeares travayles from Scotland to the most famous kingdomes in Europe, Asia and Affrica (Lithgow 1632).

(8.) The loss of female power accompanies many societies’ conversion to monotheism. As Tom Robbins puts it, Christianity is “a system for turning priestesses into handmaidens, queens into concubines, and goddesses into muses” (Robbins 1984:51).

(9.) This antidiarrheal medicine, called mustachoma, is made of clay and grape juice boiled to a syrupy consistency.

(10.) In the 1980s, Kaopectate’s manufacturers switched the active ingredient from kaolin to palygorskite, a clay with similar absorbent properties. In 1993 the formula was again changed, due to a lawsuit by the State of California contending that the lead levels in palygorskite were dangerous. This time, bismuth subsalicylate, the same active ingredient in Pepto-Bismol, replaced palygorskite, rendering “Kaopectate” a misnomer. These days, if you want clay in your Kaopectate, you need to go to Canada.

Clays do continue to be sold in other over-the-counter and prescription antidiarrheal medicines: Diarrest, Di-gon II, Diatrol, Donnagel, Kaopek, K-Pek, Parepectolin, and Smecta. Most of these are not available in the United States.

(11.) Veterinarians used to recommend that pet owners use Kaopectate to treat their pets’ diarrhea, but because bismuth subsalicylate is an aspirin derivative, Kaopectate is no longer safe to feed to your furry friend. Palygorskite is, however, available in the United States for animal consumption in a product called Dia-sorb.

(12.) Smecta™ is rarely used in the United States, for reasons I do not understand.

(13.) Much of the information in the rest of this section is drawn from Reinbacher (2002).

(14.) Clays have, however, been used in various health movements (e.g., Knishinsky 1998; Post-Dispatch 1902). For example, in 1902, seventy-five men and women were persuaded by St. Louis resident William Windsor to eat a daily dose of earth (p.176) (Post-Dispatch 1902). From the journalist’s description, Windsor sounds like an endearing armchair scientist. “Kris Kringle himself is not a more rotund nor more rollicking character than Dirt Eater Windsor…. He can sit in a chair and tweedle his thumbs on his stomach, which they say is the pièce de résistance in happiness.” Windsor explained his decision to become a geophagist. “I wondered why men were not as healthy as animals. I observed that almost every man had stomach troubles and that the wild animals had good stomachs. I became convinced that their good health was due to the fact that they were dirt eaters.” He then tried it and experienced “such great success” that he began teaching dirt-eating. The dirt he and his adherents ate came from river bottoms, and was sterilized and distributed at a cost of about 10 cents/week (approximately $2.50 in 2010). He carried a sack with him wherever he went, and clearly relished it. During the interview, he took a heaping spoonful and “swallow[ed] it with that sly wink with which a Kentucky colonel takes his whiskey. He [sent] a glass of water to chase it, and heaves a huge sigh of content.”