The use of sorrel in treating plaster is a very old recipe. Its origins are uncertain, but the best that I can guess based on the review of European writings on this particular recipe, it appears to be of Germanic origin, with the oldest links pointing to sometime during the 1600s, with possibilities of even earlier routes. The recurring nature of this recipe says to me that it is much more a folklore derived from domestic traditions than anything to do with medicine as its own profession.
There are two major recurring forms of this recipe and a few side branches to this tradition. The first and oldest form of the recipe involves the use of Oxalis, also known as sorrel or wood sorrel. We can add as well the other “sorrel” plant not at all related to oxalis that has similar properties–Rumex acetosella and Rumex acetosella. Each of these sheep sorrels also contain a significant amount of the oxalic acid needed to make the leaves sour, and a poultice of the plant capable of “dissolving away” old tumors and masses of diseased tissue.
In general, acid rich plants make them good for this use. But there are a number of cancer plaster or poultice recipes that lack this acidity, that also came to be known as cancer remedies. The first of these is the clover leaf recipe using a Trifolium species. The Trifolium lacks any significant oxalic acid, so the acid-related benefit is now no longer an important part of the philosophy of the promoter, stating how and why this remedy should work. The addition of another oxalate source like Dock (Rumex sp.) helps to reduce the validity of this argument somewhat, but still, the formula is not as acidic as it once was due to the sorrels. During the early to mid-1800s, Samuel Thomson made this recipe fairly popular and it is very commonly mentioned for use as a “cancer” remedy.
Another branch of this philosophy pertains to other plants, somewhat acidic, but more importantly more toxic that oxalis when it comes to rteating diseased flesh. The rhubarb in particualr fits this situation. The Chinese rhubarb in particular has quite a violent effect upon normal healthy tissue due to its oxalate in combination with its anthraquinones. It is the anthraquinones in particualr that seem to relate to this flesh-eating toxicity. If acidic enough, the application of this plant concoction to the surface of a “tumor” would helpt to eat away the flesh, while the anthraquinones work to kill off the freshly exposed cells beneath, producing more mass for the acidity to eat away. This makes rhubarb a more influential medicine (I wouldn’t say effective), but it has a reduced acidity so will not tear away at the flesh as quickly as a physician might like.
A third branch of this philosophy has to do with the use of certain other truly effective cancer remedies for treating the supposed “cancer” cases being presented. In particular, podophyllum is the most effective of these true cancer drug containing plants. But interestingly, podophyllum was never really know to be a cancer drug until the early 1900s, sometime between 1920 and 1940. This is because the true nature of cancer was not known. Podophyllum’s most importantu se from 1880 to the late 1970s was as it was first proposed in the nineteenth century–as a liver remedy at first, and a laxative later. The most important example of this is Carter’s Little Liver Pills, which by the 1960s was sold a Carter’s Little Pills or just Carter’s Pills.
These very small round pills were so effective because the podophyllin is very toxic on the intestinal lining. They kill the intestinal lining cells, which then results in irritation and increase motility. They irritate the biliary duct causing bile to be extruded into the gut, and thus the yellowing of the stools. And by killing older cells it causes them to slough off more frequently (the longevity of an intestinal wall cell is about 2 weeks), resulting in fluid loss and at times very liquidy stools. In essence, any intestinal lining poisoned as much as it was by something like podophyllin was bound to become quite purgative and motile in its activities. Some of the other plant-related laxatives work in a very similar way–such as the anthraquinones Cascaroside from Cascara and Sennoside from Senna.
So all previous examples of cancer drugs it ends up weren’t exactly treating true cancer, just a cancer like condition such as an abscess or other form of inflammation and swelling. So, the “cancer drugs” of the earliest years weren’t cancer drugs at all–just flesh-eating plant formulas, something anyone could actually come up with within a domestic environment given the right acids and alkali. And those that are contained in the related true clover related recipes, nopt cancer drugs at all, but probably a consequence of some early herbalists assuming oxalis and true clovers were so closely related due to similarity in appearance, that the use of oxalis could be modified and applied to the non-oxalic acid rich Trifolium species. [see Transformation of Common Belief writings.]
Now, these recipes never fully diminished in value due to this misinterpretation of disease and the effects of the remedy. Two plant acids are very commonly used to treat conditions where skin mass is a problem–plantar’s arts and thick calluses. The two organic acids employed to treat these conditions are oxalic acid and salicylic acid. The larger the molecule of the acid, the more likely it is to be a tolerable use of the acid. Oxalic acid tends to be more damaging that salicylic acid, which is why these recipes have in recent decades concerted to salicylic acid based formulas.
Another common reason applied to the preferred use of salicylic acid over oxalic acid is that the first is related to aspirin and therefore has some appliative effects as well such as the reduction of pain and swelling. This is not really the case for salicylic acid. Acetylated salicylic acid does have such an effect due to the acetyl group–remove that group and you lost your anti-inflammatory effect or at least reduced it down to about 5 or less of what it was. There is this common myth going around in the plant medicine world about this misassociation of salicylates with aspirin or spirin and the salicin analogs or chemical similars. Thie is like saying linoleic acid is just as healthy as linolenic acid and will work just as well, so why spend the extra money on the evening primrose, flaxseed or ribes oil?
Examples of these recipes:
From Worthy, A.N. A Treatise of the Botanic Theory and Practice of Medicine, compiled from various sources, with revisions and additions. Forsyth, Geo: C.R. Hanleiter, 1842.
Note: The Forsyth, Georgia school was more truly Thomsonian in nature than its contemporary Physiomedical rivals.
Cancer Plaster [p. 616]
“Take of red clover blossoms, four pounds, and roots, or roots and tops of narrow dock, one pound. Or any larger quantity in the same proportion, boil in water until the strength is out, then separate the clover and dock from the liquor, carefully pressing all the juice from them, and return it again into the kettle, and continue the boiling with the utmost care to prevent burning, until reduced to the consistence of a salve or plaster.”
Sorrel Plaster or Salve [p. 616]
“Take the common sheep sorrel, any quantity, bruise, and press out the juice, place it in plates in the sun, until dried away to a proper consistence for a plaster. This may be applied to the cancer, spread on paper, or a piece of bladder made soft, and must occasionally be renewed. If it proves too painful, it may be left off at night, and re-applied in the morning.”
Cancer Balsam [p. 616]
“Take of sorrel salve, balsam fir, and salt butter, of each equal quantities. Mix Applied as the above before.”
Dr. S. Thomson’s Cancer Plaster 
Take of the heads of red clover sufficient to fill a brass kettle, and boil them in soft water for one hour; then remove these from the kettle, pressing the liquor out from them, and fill the kettle again with fresh heads, which must be boiled in like manner in the same liquor, adding as much more water as may be necessary. After boiling these about an hour, the liquor must be strained off and the clover heads pressed as before to get it all out. Then return it into the kettle and boil or simmer down to the consistence of thick tar. Very great care must be taken in boiling it down to prevent its burning; as by burning, not only the burnt part is destroyed, but the remainder is in some measure deprived of its medical properties.
When used, it should be spread upon a piece of bladder, suet skin, thin cloth, or strong paper.
Other formulas for preparing cancer plasters, may be found under the head, “Cancer.”
Oxalic acid conjoined with the above, in the properties of eight parts of the balsma to one of the acid, (the two ingredients put into wedgewood mortar and thoroughly incorporated) is a valuable adjunct.
[It will be remembered the acid is prepared from the sorrel.]
Wood Sorrel (Oxalis sp., O. acetosa, perhaps O. acetosella) Fam: Oxalidaceae
Pacific Coast Journal of Homeopathy vol. 1, no. 4 (April 1893), p. 148.
“Wood Sorrel in Cancer.”
Dr. George Walker, Medical News, recalls a case in which he treated “an old woman” and cured her of “at least cases of epithelioma with oxalis acetosella.”
The medicine was prepared:
“in which she expresses the juice [of oxalis], pouring it into a pewter-plate, and allowing it to evaporate in the sun until it becomes a solid extract.. The mass is then scraped away, and a part is applied to the diseased surface. Great pain appears in about twelve hours, and a few hours later, considerable swelling is developed, both continue for about four days. On the fifth day, sloughing begins, a mass of diseased tissue falls out in one piece, later smaller portions slough away, leaving a clean, healthy-looking ulcer, which rapidly heals.”
The history of this use of oxalis, according to the author, relates to the medical lore regarding its use by common people in the “old country, especially in Germany… [where] this plant is highly prized as an excellent medicine in affections of a malignant character, and, also in dysentery.”
From Russel Crawford’s trail diary, ca. 1852-7 (also reviewed on another page on this site)
For a Cancer
Obtain a large quantity of the herb known as Sheep Sorrel, Bruise it until the juice can be pressed out, by pounding it well. Press the juice out of the herbs and strain it. After straining it put it in a pewter plate or vessel and place it in the sun; the acid will combine with the pewter and form a salve which being applied as a plaster will eat between the cancer and the sound flesh and it can be extracted in short time.
A Food on the Oregon Trail mishap
In a book published a number of years back on foodways and the trail, a physician was noted to be collecting and drying the leaf of a local trail plant for later use. The author supposed this to be for food, but in fact due to the toxicity of this plant is was more likely going to be used as a medicine. It ends up this Croton plant is a Euphorb or Spurge and is quite toxic and capable of producing a flesh-burning plaster if prepared properly. The Croton plaster is more often used to apply to a chest wall, in order to draw fluids outward from within, as if removing the fluids from the lungs then thought to be a cause for consumption. Due to their ability to cut into flash, spurges are also common thought of as “cancer remedies.”
A mid-colonial substitute
One common plaster of potential use for treating “cancer” is formed using the bark or inner bark of Dirca palustris, Leatherwood. This plant is not mentioned much in the mid-19th century Midwestern history however, so is not covered beyond this brief mention. Its chemistry makes it an irritant and a very effective blistering agent.
The sorrel plasters were developed during the mid- to late-colonial period in North American history. Plants of the Polygalaceae family are also capable of causing blisters, but no specific uses are found for most of them, excluding the Polygala senega o0r Seneca Snakeroot for snake bites.
Other possible “cancer” drugs
The following plants have a direct or indirect history of use for treating “cancer”, not the true cancer, only the “tumors” and other flesh-like conditions remesmbling true cancer.
- Pokeweed (Phytolacca sp.) [see Cadwallader Colden's review of this.]
True Cancer Drugs
The following plants have phytochemicals that are true cancer drugs, that is to say they interrupt cell division processes and prevent a tumor that is malignant from dividing at the same speed, or at all:
- Calocedrus sp. – epipodophyllotoxin
- Taxus baccata – taxol
- Thalictrum spp. – thalictrine, thalicarpine
- Sanguinaria canadensis – sanguinarine or zeta-homochelidonine
- Podophyllum peltatum – podophyllotoxin
- Chelidonium sp. – homechelidonine
- Celastrus scandens -