鈥淪ince calomel鈥檚 become their boast,/ How many patients have they lost?/ How many thousands they make ill,/ Of poison with their calomel?鈥� So ran a little verse written in 1825 by an unknown poet who was obviously disenchanted with medical practice of the day. 鈥淐alomel鈥� was the curious name given to mercurous chloride, Hg2Cl2, the most common medicine of the era.聽Why curious?聽Because the name derives from the Greek 鈥渃alos鈥� meaning 鈥済ood,鈥� and 鈥渕elas鈥� for 鈥渂lack.鈥澛燱ell, calomel was neither black nor good.聽The 鈥渂lack鈥� is thought to refer to the precipitation of finely dispersed black metallic mercury when calomel reacts with ammonia and the 鈥済ood鈥� was what calomel was supposed to do for a sick person.聽
The writer of that little poem, who could have benefited from a rhyming dictionary, had the right message.聽Calomel didn鈥檛 cure people, it made them ill.聽How is it then that calomel, along with other metal salts, was commonly used by physicians for some five hundred years as standard therapy for almost every disease?聽
First, many diseases are self-limiting and resolve by themselves.聽But when calomel was given, it got the credit.聽Second, the belief that it would help was often enough to make a patient feel better.聽The 鈥減lacebo鈥� effect is very powerful indeed.聽Third, patients were often so sickened by calomel that they professed to feeling better just to avoid further therapy.聽Fourth, people who succumbed to calomel poisoning were not around to register complaints about the treatment.聽And finally, in rare cases, mercury compounds may actually have cured a disease.聽Mercury can poison all kinds of organisms, including bacteria.聽Syphilis was a bacterial scourge throughout history, and if a physician happened to get the dose just right, mercury compounds sometimes killed the bacteria without killing the patient.
The use of mercury to treat disease can be traced back to Paracelsus, the sixteenth century physician, alchemist and philosopher.聽At the time, medicine was based on the ancient Greek idea that health was a reflection of the balance between the four humours, namely black bile, yellow bile, phlegm and blood.聽Paracelsus decreed that this was bunk, and expressed his disgust of the uncritical reliance on ancient authorities by publicly burning their works.聽He insisted that the physician should explore the world and learn from nature.聽 For every disease nature provided a cure, Paracelsus suggested, and the physician鈥檚 role was to find it.聽And in mercury compounds, he thought he had found a cure for many conditions.聽To his credit, though, Paracelsus recognized that mercury could also be a poison, and insisted that dosage was critical.聽Indeed, his dictum that 鈥渙nly the dose makes the poison,鈥� is still the cornerstone of toxicology.聽But he never realized how little mercury it actually took to cause a great deal of harm.聽
Where did Paracelsus and his followers get calomel?聽They had to prepare it from cinnabar, naturally occurring mercuric sulphide.聽Heating this red ore in air drives off the sulphur as sulphur dioxide and leaves behind shiny mercury metal.聽Treatment with sulphuric acid, prepared since ancient times by heating naturally occurring iron or copper sulphate, forms mercuric sulphate, which in turn, when heated with ordinary salt produces mercuric chloride, a white powder with formula HgCl2.聽
To Paracelsus, the production of a white crystalline substance after all that messy and smelly manipulation must have seemed astonishing.聽Could this be one of the elusive substances that nature provided for mankind鈥檚 benefit?聽There was only one way to find out, try it.聽Without doubt, mercuric chloride had an immediate effect.聽The patient gave up the contents of his bowels quickly, a sign that disease was being driven out of the body!聽And so began the age of 鈥渉eroic medicine,鈥� characterized by doctors attempting to bludgeon the disease out of the patient.聽
Mercurials and antimony compounds evacuated the digestive tract in both directions, and were often coupled with blood letting to rid the body of disease.聽Often, they rid the body of life.聽Particularly when the highly toxic mercuric chloride was used.聽Since dead patients were not good for business, or for reputation, a safer purgative was desirable.聽Heating mercuric chloride with some more mercury, produced mercurous chloride, or 鈥渃alomel.鈥澛營t was still a cathartic, but being far less soluble than mercuric chloride, it was less toxic.
That鈥檚 not to say it was safe.聽When given over a period of time, as was common practice, calomel would cause excessive salivation, gum inflammation and various neurological symptoms.聽Patients developed tremors, balance problems and personality changes.聽But doctors lacking truly effective medications, continued to torment the ill with calomel.聽George Washington was administered it on his death bed, probably hastening his demise.聽
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