THEORIES OF MEDICINE IN THE 18TH CENTURY

 

During the 16th, 17th and 18th century there was steady progress in the field of anatomy and in surgery. As is shown in the article on classification of diseases, this was often based on symptoms rather than underlying diseases. A headache for example might be the result of a cold, a migraine, high blood pressure, meningitis or a brain tumour, each requiring a different treatment rather than a "cure for headache". When it came to theories of disease and treatment one cannot say that there was steady progress in the 18th century. There were a number of theories that did not advance the subject, many mercifully did not outlive those that proposed them. While advances in the knowledge of anatomy had improved surgery, the subjects of physiology and chemistry were far too primitive in 1800 to give much aid to medicine.

Brunonian Theory

John Brown (1735-1788) was a doctor in Edinburgh. He published his theory in 1784 proposing that there were two types of disease. Those with too much excitation (sthenic) and those with too much depression (asthenic). He proposed treatment with opium to quieten or alcohol to excite.

Methodist School

Democritus was the first to propose that every substance was made from small indivisible particles called atoms. This idea was incorporated into medical ideas of Asclepiades (128-50 BC). Two types of disease arise - when the atoms are too widely spaced (morbus laxus) or too close together (morbus strictus). In the former case one should use heat, laxatives or blood letting so that the atoms move closer together, whereas in morbus laxus one should use cold, or astringents such as alum.

The Doctrine of Similars

Paracelsus (1493-1541) was a supporter of the views of Hippocrates and believed in vital force. He accepted the idea that diseases can be cured by medicines similar in nature to the disease. For example a yellow material such as yellow feathers could be used for treating jaundice.

Doctrine of Contagion

The Doctrine of Contagion, not to be confused with later ideas on infectious diseases, had features parallel to the Doctrine of Similars but looked for materials that might be connected with the origin of the disease. Thus, moonstone must be good for lunacy where people were believed to be under the influence of the moon.

The Doctrine of Signatures

Paracelsus devised the Doctrine of Signatures. Materials useful in medicine could be recognised by their shape, size, colour, or taste. For example heart shaped leaves were good for the heart and liver shaped leaves useful in treating the liver. Walnuts were good for the brain and kidney beans for the kidney. This theory was also supported by Nicolas Culpeper (1616-1654) whose use of plants was based in part on astrology. For example a disease might be associated with one planet such as Mercury or Venus and should be treated by a plant that came under the influence of a complementary planet.

Doctrine of Analogies

Attempted to deduce cures from the behaviour of sick animals. Cures were of divine origin and if God provided them for animals, He would provide for mankind.

Iatro School

Phenomena of life based on chemical action and on laws of physics. Archibald Pitcairn (1652-1713) and Boerhaave at Leyden were proponents of this very advanced school of thinking. It is the scientific principle on which medicine is based today but in the early 18th century the understanding of chemistry, biochemistry and physiology was far too primitive to allow progress to be made..

Pneumatic Theory

Athenaeus, 1st century AD. The theory was that pneuma or vital air was circulated around the body by the blood. Strength of pulse indicated good health. There was no knowledge of the circulation of the blood at that time. Blood was thought to ebb and flow like the tide with each pulse. However, the recognition that blood played an important role in delivering nutrients to the tissues was along the right lines.

Humoral Theory

This theory came from the ancient world and tends to be associated with Galen, the Greek physician of the Roman Emperor, Marcus Aurelius. University training for medicine required knowledge of Galen and Hippocrates well into the 19th century. The origins of the theory lie with Aristotle's view that the universe was made up of four elements - fire, earth, air and water. Associated with these were four properties, hot, cold, wet and dry. Thus fire was hot and dry, water was cold and wet, air was warm and wet and earth was cold and dry. Clearly Aristotle would have had different ideas if he had lived with the English climate. This almost magical system of fours was extended to the human body, which had four humours.

Blood leading one to be Sanguine
Phlegm leading one to be Phlegmatic
Bile leading one to be Choleretic or Jaundiced
Black bile leading one to be Melancholic

The exact nature of black bile is uncertain but may have related to blood in vomit or faeces.

Adjustment of the humours involved withdrawing body fluids by various means as follows:

· Bleeding, by venesection, cupping or leeches
· Raising a blister and bursting it
· Using emetics to make the patient vomit.
· Using laxatives and purgatives to empty the intestinal canal and in some cases cause vomiting too.
· Use of agents to cause sweating (diaphoretics or sudorifics)
· Increasing urine flow with diuretics

The Indian Ayurvedic medicine system has similarities to the humoral theory but invokes five elements instead of Aristotle's four; the fifth is the "ether" or space in which everything happens. This system is part of a much wider philosophy but the ancient medical practice uses massage, emetics, purges, enemas, sweating, nasal administration of medicinal oils and blood letting.

Homeopathy (1810) "Like cures like" Samuel Hahnemann (1755-1833)

Hahnemann was horrified by the blunders of medicine in his time such as treating people with mixtures of powerful purgatives and emetics that often produced spasms and cholic treated by belladonna - resulting in further ill effects.

His "theory" was that you treat with a drug producing the same symptoms, but in very small quantity and in this regard was similar to the doctrine of similars. The theory is doubly flawed. In the first place symptoms are not the same as diseases - a headache may be the symptom of influenza, meningitis, a brain tumour, high blood pressure or a migraine. Each requires a separate treatment rather than a cure of headache.

His theory that the more dilute a medicine the more powerful it is runs counter to all scientific work of the last two centuries and to everyday experience of everyone in their working lives and homes. If you wish to dye some cloth and find the colour not sufficiently deep, the next time you do it with more dye not less. When the washing up contains many greasy plates, you use more washing up liquid than usual not less. The effect of any substance is proportional to the amount used. All industry depends on this phenomenon and reliably delivers a huge range of products.

The dilutions used for homeopathic remedies are such that the final concentration of agent is nil. For example if one were to start with 58 grams of common salt, it contains 6 times 10 to the power of 23 molecules of sodium chloride (Avagadro's Number). If you were to dissolve this in say a litre of water and then perform a 100 fold dilution (10 millilitres into 1 litre) 20 times it would be diluted by ten to the power of 40 leaving on average less than one molecule of sodium chloride in the final sample. All the sodium chloride would be in the discarded 990 millilitres of water from each dilution.

A review in ‘The Lancet’ of 90 clinical trials producing inconclusive results with homeopathic medicines concluded that it was time to stop wasting money on placebo controlled trials of pure water versus pure water. In the case of homeopathy, the placebo effect is enhanced by the use of archaic terms. For example common table salt is now known as sodium chloride with formua of NaCl. The symbol Na comes from the old word for sodium which was natrium. Homeopathy uses Natrium Muriate, an archaic name for sodium chloride. Sodium chloride is an important constituent of all body fluids and occurs naturally in most foods even without addition in cooking or at the table. The best thing that can be said about homeopathy is that pure water has not poisoned anyone. However, faith in the curative powers of pure water has prevented many from seeking medical advice until it is too late.

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History of Medicine
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