Iron

There are famously seven bridges crossing the Tyne, linking Newcastle-upon-Tyne to Gateshead. This is a selection of them. I was hopeful of a  catenary curve
for the collection I'm compiling with blipper MsMun, but I can't find any hint that any of them contain one. The most hopeful, I thought, is the millennium bridge - the 'blinking eye', the first tilt bridge ever constructed - that is in this picture as an elegant, narrow white arch spanning the river in the distance. It turns out that its shape is not catenary, but a closely-related parabola

We spent a while over supper discussing haemochromatosis - a genetic condition that causes the body to absorb too much iron from food, leading to a build up of the body's iron reserves in the blood, in the form of a compound called ferritin. (Blood haemoglobin also contains iron, but that is unrelated to the condition). Prolonged exposure to excess ferritin in the blood damages several organs: liver, pancreas, heart and joints. Diabetes can be a secondary symptom. 

It is easily treated by regularly taking some blood from an affected person, just like a blood donation, but it is often not diagnosed until organ damage has occurred. The causal mutation is particularly common in people with Celtic family history, so it is known as the 'Celtic curse'. We know personally two people who are afflicted, both with Celtic roots

How fundamental to us iron is. The earth's iron core generates the magnetic field that makes life on earth as we know it possible. Iron is the basis of chlorophyll - the green molecule that catalyses photosynthesis in plant leaves, without which most plant and animal life could not exist. Iron is at the centre of the haemoglobin molecule that carries oxygen around the body of many animals, including us. And iron builds bridges across the Tyne. But the same element is capable of turning against us and killing us. Handle with care