Wednesday, 19 January 2011

Chemical Elements

David Pirie, Medical Herbalist at the Tara Trust in Edinburgh came to the Gardens this week to give us instruction in plant chemistry; specifically the actions of primary and secondary metabolites. In a Socratic tradition our first proposition was to argue the premise of the topic – is it the chemical constituents of plants that are solely responsible for any physiological changes (and by extension, healing) in the body? Or is it the plant’s energy that affects healing? For intstance, South America herbalists match the sound resonance of a plant to a person before prescribing anything…so here we go

It actually all comes down to your gut reaction. Or rather the GIT (gastro intestinal tract) and how the metabolic process transforms foods /herbs in transit through the stomach, liver and bloodstream into the chemical compounds that nourish and heal.  Each plant’s chemical structure has a different action on the body, is released in different ways, works at its own pace and leaves when its ready.

Dr William Withering
with Digitalis
Dr William Withering discovered this in his seminal work with Dropsy patients prescribing the hitherto deadly Foxglove (digitalis). He realised that each patient required not only a different dosage depending on their tolerance but critically that dosages should decrease as heath improved. (The first dose of any toxic plant will make you nauseous – this set the dose for each individual).

Plants contains thousands of chemicals, categorised as metabolites: primary ones necessary for a plant’s survival and propagation; and secondary metabolites which are non-essential but that add a colour, flavour, aesthetic or action that contributes to its overall form. We often use only one part of a plant to deliver a specific healing action, but many herbs are best used holistically, balancing a potentially dangerous or toxic effect of a primary metabolite with a secondary one.  


It is these secondary metabolites that we turn to supply the key active ingredients in the healing process. They can be categorised most broadly as:
  • Acids
  • Alkaloids
  • Carbohydrates
  • Glycosides
  • Isoprenoids & terepenes
  • Phenols
  • Amines
  • Rubber Polymers
  • and so on...
David expounded on these further, breaking down each into its primary action and uses (anti-inflammatory/ antiseptic/ mucillangenous, etc), its relationship with key internal organs, what plant were sources and any potential complications. 

Naturally we wandered in our discussions, pondering how smell might be the most powerful influence on the human brain, what influence emotional memory had and new thinking in psycho-neuro-endo-immunology….

Last session of the day took it all and gave us one last twist – how elements of taste should also be considered in understanding treatments. The Chinese believe that a person’s life energy (Qi) runs along meridians in our body, linking and affecting all our organs. Each organ in turn is associated with an element (Fire, Water, Earth, Air, Metal) a season, an emotive state and a taste (sweet, sour, salty, bitter and pungent). By understanding the relationship of these elements we can adjust the Yin/Yang balance to maintain and obtain optimum health. 
 Diagram of the 5 Elements

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