Instead, infections were believed to be spread by Miasma, a nasty smell. It was only when microscopes came into existence, and bacteria could be seen, that medical thinking suddenly changed. ‘Oh, look.’ Maybe John Snow was right after all.

Galen must have known that the heart was a pump of some kind, with chambers and valves. But if you trace the blood vessels out from the left side of the heart they become smaller and smaller until they simply disappear. They certainly cannot be seen by the naked eye. How can blood possibly flow through non-existent channels?

Given that there was no way – at least none that he could see – for the blood to flow through organs and tissues, Galen decreed that when the blood arrived at the tissues it was used up. Gone, in a puff of smoke… and for my next magic trick.

Would you or I have thought the same thing? Or would we have paused for a moment. Hold on, there must be very small blood vessels in there somewhere. After all, the heart pumps about a gallon a minute. No way can the liver possibly be manufacturing that amount. Nor can the tissues be using up that much. That is just not going to happen.

Several of Harvey’s experiments to disprove Galen’s idea were quite simple. They involved cutting open an artery in an animal to see how long it took for the blood supply to run out. Not long, as it turns out. As all butchers of the time knew.

Another problem with Galen’s model, that you might already have spotted, is that for it to work, blood had to be able to pass straight through the heart, from the right to the left, through a muscular wall – the septum. For this to be possible it had to travel through invisible pores.

So, Galen managed to convince himself that there were tiny invisible pores within the heart. Yet there could not possibly be invisible pores throughout the rest of the body? This is another feature of medical thinking. A (wrong) idea becomes widely accepted as the truth. In time, more and more contradictions turn up. However, rather than being discarded, the idea twists and turns, and grows and distorts, in order to keep it alive.

This can, perhaps, be most clearly seen with the cholesterol hypothesis. It began life as ‘high cholesterol causes heart disease.’. When populations were found that had high cholesterol levels and low rates of heart disease the hypothesis was not discarded. For, by this time it had become an established medical fact.

Instead, it transformed into the ‘good’ and ‘bad’ cholesterol hypothesis. Then, the total cholesterol/HDL ratio… hypothesis. The small and dense LDL hypothesis, the non-HDL hypothesis, The small dense, light fluffy LDL hypothesis, the cholesterol particle number hypothesis, the oxidized cholesterol hypothesis the…take your pick, there are hundreds of them nowadays.

Each one represents an attempt to explain a contraindication to the new, adapted, hypothesis. I have to say that I have found it difficult to stamp on something that simply will not keep still. It just changes shape and moves somewhere else at high speed, whilst still managing to remain as the same hypothesis… in some way. Sigh.

Returning to the ‘if you can’t see it, it doesn’t exist’ problem, let us travel forward in time from Harvey, four hundred years, or so.

Here we arrive at the Coronary Artery Bypass Graft (CABG). At this point we find ourselves in a world where vast sums of money were being made by cardiovascular surgeons carrying out this procedure. Many were raking in millions each year. See under ‘bleeding and purging’. This is what Bernard Lown had to say on the matter of CABGs.

“Forty years ago I stopped referring most patients with stable coronary heart disease (CHD) for cardiac angiography.) This procedure permits visualizing the extent of obstructed coronary arteries. What occasioned my deviation? The problem was that nearly all those undergoing angiography ended up having surgery, namely, coronary artery bypass grafting, or CABG (pronounced ‘cabbage’).

“What could be wrong with improving blood flow to the heart by unblocking an obstructed or narrowed artery? Such a seemingly commonsense approach would have had the approval of every plumber who encounters a blocked faucet.

“But, first of all, the heart is not a plumbing fixture. When a coronary vessel is narrowed or blocked, the heart has a built-in defense mechanism: It develops a collateral network of small vessels to compensate for the diminished delivery of nutrients and oxygen.“ [4]

I urge you to read this essay. It is by one of the absolute greats of medicine, and a hero of mine.

The main point I wanted to highlight here is not just the money being made from CABGs – which always represents a formidable barrier to progress. The more important barrier was that doctors found themselves transfixed by the large arteries that supply blood to the heart. If they were narrowed, this was obviously a disaster, as blood flow to the heart muscle was seriously impeded, and a heart attack was imminent. The artery must be bypassed immediately using a bypass graft.

What they seemed blissfully unaware of is there is a way for the blood to reach the heart muscle, even if the large artery was narrowed. Which is through invisible ‘pores’ – something called collateral circulation. Collateral circulations allow blood to flow through minute blood vessels that are too small for the human eye to see. Even if, by the mid twentieth century, they were not technically invisible. Everyone could see that they existed. If, that is, they chose to look.

But cardiologists focussed entirely on what they could see… ‘Big artery, narrowing, bad…must treat.’ Did it work? In an acute blockage, such as occurs in a heart attack. Yes it did… Otherwise…no. Not really, or not at all. Depends on which of the thousands of clinical papers you read. Here is the summary of one article from Stanford Medicine.

“Patients with severe but stable heart disease who are treated with medications and lifestyle advice alone are no more at risk of a heart attack or death than those who undergo invasive surgical procedures, according to a large, federally funded clinical trial led by researchers at the Stanford School of Medicine and New York University’s medical school.” [5]

This study looked at CABG, and stents (small metal tubes inserted into coronary arteries to open them up). They found that for the great majority of people, they simply do not work. As Bernard Lown had established over years previously.

As you can see the ‘if you can’t see it, it doesn’t exist’ fallacy has not gone, and probably never will. It continues to drive many areas of medical thinking, and remains a recurring theme.