Eating Dirt and Terra Sigillata

"A cloak of loose, soft material, held to the earth’s hard surface by gravity, is all that lies between life and lifelessness."

-- Wallace H. Fuller, Soils of the Desert Southwest, 1975

El Santuario de Chimayo, New Mexico. Credit:

Dirt is a paradox. Children playing in the dirt all day are admonished to wash their hands before eating dinner. But eating dirt, or geophagy, has been pervasive throughout centuries and across diverse cultures. I learned last week while at the Santa Fe Science Writing Workshop that northern New Mexico is home to soils used for religious purposes. El Santuario de Chimayo, a Catholic shrine and pilgrimage destination, is home to a small pit of soil called El Pocito. Legend has it that in 1810 a local friar saw light bursting from a hillside and found a crucifix when digging to identify the source. Since then the soil in the hole has been believed to impart healing properties. The legend is so pervasive that Gerald Callahan used the story to launch a 2003 article in Emerging Infectious Diseases, a publication of the US Centers for Disease Control and Prevention. But one needn't make a pilgrimage: you can order your holy dirt of Chimayo here. Alas, one is advised today that the dirt is not to be eaten or drunk, although other information on the website indicates that has been on use of the soil. Twitter follower and Charlotte-based CEO of Molecular Creativity, David Bachinsky, alerted me the other day to a press release on a forthcoming paper that explores the reasons for eating dirt. Sera Young and colleagues at Cornell University explored nearly 500 cultural accounts from missionaries to anthropologists to determine the most likely of the three choices. The analysis will appear next month in a Quarterly Reviews in Biology entitled, Why on Earth?: Evaluating Hypotheses about the Physiological Functions of Human Geophagy. Three main hypotheses have emerged to account for this practice first described by Hippocrates over 2,000 years ago:
  • To reduce the pangs of hunger
  • To provide minerals lacking in the diet
  • To protect against parasites, pathogens or naturally-occurring toxins
My apologies to the reader that I am only going off a press release but I have requested the embargoed original paper since this topic is near and dear to this blog. I'll discuss the hypotheses and outcomes in another post after I've read the paper. However, my interest was also piqued by mention that Young has also written a book for popular consumption (pun intended) entitled, Craving Earth: Understanding Pica -- the Urge to Eat Clay, Starch, Ice, and Chalk. But this story also gives me the opportunity to repost the original explanation of how I chose Terra Sigillata as the name for this blog. What follows is a periodically updated post that ran originally on 20 December 2005 at the blog's first home at Blogger.

Original blog banner designed by Brien O

Why Terra Sigillata?

Updated 7 June 2011

If you Google, "Terra Sigillata," you'll get a number of hits for various clay pottery recipes. It's made by a differential sedimentation process of clay - very complicated stuff - requiring the use of a deflocculant to separate out large clay particles from the small ones. Terra sig, as it is known among pottery hipsters, is then used to coat finished pieces to produce a very smooth, high luster and waterproof finish. Since originally writing this explanation nearly five years ago, clayworkers and other artists who've stumbled on the post have directed me to some of the many variations on terra sigillata. The best so far has been this copyrighted recipe and description by Vince Pitelka at the Appalachian Center for Craft at Tennessee Tech from research he had done since teaching ancient clay arts classes at the UMass-Amherst. Take a read later on because the process is really an ancient chemical method and is quite fascinating. What does this have to do with pharmacology and natural products? Terra Sigillata is a Latin term that literally means "sealed earth." In the common potter's vernacular, the term is used to describe its use as a high-lustre seal on clayworks due to the uniform orientation of kaolinite crtystals. But, in ancient pharmacy history, Terra Sigillata refers to the first trademarked drug product, a small clay tablet or planchet bearing an official mark of authenticity. In this case, the "seal" was a mark for trade and marketing purposes. Those of you with pharmacy backgrounds may also know that the notation for dose, duration, and route of administration on a prescription is abbreviated, "Sig.," short for Signatura, meaning to sign, seal, or mark. Dirt as medicine Yes, pre-Christian cultures ingested dirt (but only special dirt) as medicine. (Admonishment from my soil scientist colleagues: I meant to say, "soil" - sorry.). The medicine known as Terra Sigillata began as a unique clay first harvested around 500 B.C. from a particular hill on the Mediterranean island of Lemnos, now part of Greece. Dug on a special day annually in the presence of governmental and religious dignitaries, the clay was rolled to a defined thickness and pressed with an official seal by priestesses and dried in the sun. Kind of reminds me of my favorite beer, Samichlaus, brewed once a year on 6 Dec. Known as geophagy today, the practice is not as odd as it sounds and is common to primates. Today, we now know that clays contain kaolin (an active antidiarrheal component formerly in Kaopectate), minerals like iron oxides and others like calcium carbonate and magnesium hydroxide that may have served as nutrients or antiacids. Moreover, various ethnomedical cultures have encouraged clay consumption by pregnant women, both to ease nausea and to adsorb dietary alkaloids and steroids present in the plant diet from harming the developing fetus. Having lived in the southern US for a third of my life, I'm also aware the red clay of the southeastern region is highly regarded for settling the stomach. According to John and Dale Reed in "1001 Things Everyone Should Know About the South," the practice of geophagy seems to have originated in Africa and was widespread in the 19th century South among the poor of both races. The Reeds claim that the taking of the clay is the source of "sandlappers," a nickname for South Carolinians. Heck, I've even heard Michael Stipe of R.E.M. (and Athens, GA) remark that red clay is in his blood, although I suspect his claim may be more figurative. The inspiration I learned of all this great history when I began leafing through a classic 1965 pharmacy history book, "Great Moments in Pharmacy History." (Washington State University's College of Pharmacy received permission to post the images online; here is the painting and brief description of Terra Sigillata.) The drug company then known as Parke, Davis & Company, commissioned Robert A Thom, a Birmingham, Michigan artist, to prepare paintings of historical scenes to accompany historical text collected by Prof George A Bender from pharmacy sources worldwide.

From the Terra Sigillata entry in, "Great Moments in Pharmacy," by George Bender with paintings by Robert Thom.

It's a great book that can be found through e-tailers focusing on out-of-print texts. If you went to pharmacy school anytime since the mid-1960s, you know what I'm talking about because Thom's unmistakable portraits can be found in labs and offices in most US colleges of pharmacy. This excerpt from Great Moments described the subsequent uses of Terra Sigillata that will be of interest to many, especially fans of Pulitzer prize-winning science writer, Deborah Blum, whose book, The Poisoner's Handbook, has been one of my top reads of 2010.
In the early days, and even up to the early nineteenth century, Terra Sigillata was used as an antidote for poisons as well as in the treatment of dysenteries, internal ulcers, hemorrhages, gonorrhea, pestilential fevers, complaints of the kidneys, and eye infections. The most striking feature of this drug, however, was the way in which it was marketed, and the method of identifying it and warranting its origin from a definite source. The great demand for Terra Sigillata and the good business that the sale of these troches brought caused people in almost every country in Europe to look for similar earths. This trademarking to protect the rights of seller and buyer today has behind it the sanction and approval of some 2,500 years of man's experience in world commerce.
As I wrote yesterday, I am a natural products pharmacologist possessed of great admiration for medicinal chemistry and pharmacognosy. But when thinking of a name for this blog, I didn't want to restrict it to plants or fungi or soil microorganisms because creatures big and small, terrestrial and marine, have been used as sources for medicinal agents. I had certainly known that my predecessors had been culturing soil for novel medicinal-producing organisms since Selman Waksman first discovered streptomycin (although credit for this Nobel prize-winning discovery has increasingly been attributed to Waksman's graduate student, Albert Schatz, who incidentally grew up across the street from the Passaic, NJ, hospital where I was born). But I frankly hadn't realized that the Earth itself had been used as a medicine. Hence, Terra Sigillata is a metaphor for the fact that the Earth itself has provided medicines to various cultures for centuries. The trademarking aspect of Terra Sigillata also holds significance for thinking about how important drug branding has become in our current culture, both for the buyer and the seller. Whether declared by a priestess, a charlatan, a shaman, a late-night infomercialist, or a pharmaceutical or biotechnology company, branding carries with it some implicit guarantee of quality or assurance of purity of authenticity. But not always. That's why we write Terra Sigillata.

Author: David Kroll

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  1. Hi David,
    What do you think of this clay? A blogger in our area thinks it’s worth $100 for 8 lbs. Here’s her post on it: She’s the antivaxx person I mentioned to you recently.

    By the way, I had pica when I was anemic but my craving was for ice and until I found out I was anemic I needed ice to chew all the time. Once the anemia left so did the cravings.

  2. David,

    Sorry, but as the holder of a graduate degree in soils (who had a class from the quoted Wallace H. Fuller), your use of “dirt” made me wince. It’s “soil” when it’s outside and “dirt” when it’s inside. Thanks for acknowledging that “dirt” makes soil scientists squirm.

    I collected some soil at Chimayo several years ago and sent some to a friend from Mauritania who had recently returned home from studying in the States and was looking for a job. A day or two after he received the soil, he heard of a job with FAO. A job
    he still holds, according to a recent email.

    I enjoyed your description of Terra Sigillata. I’ve heard of geophagy and wondered about it.