Did blood-sucking leeches help to establish – at least in some eyes – the ‘authenticity’ of the Shroud of Turin?

It will take those two leeches weeks, probably months, to digest their meal… but the lady’s red blood porphyrins will survive – although probably a little altered – the way that porphyrins in Shroud bloodstains appear to  be a little altered…

It began as a posting on a forger’s modus operandimy posting earlier this morning. Not your ordinary forger, I hasten to add, but probably a monk or similar.  He no doubt thought he was acting from the best of motives in embellishing a supposed burial shroud  – Christ’s burial Shroud-  with strategically-located  bloodstains to match the Biblical account.

Spear wound, left side, showing blood (“blood”?) but no obvious wound. This is typical of all the other sites on the Shroud that show “blood” whilst having no unequivocal evidence in the body image of there being a wound.

(How many times have we been told that the bloodstains could only have come from the crucifixion of one man – Jesus Christ – as shown by the “spear wound in the side” (just puddles of blood actually, no wound that I can see with Shroud Scope), the blood on the forehead and hair from the ultimate authenticating  detail – the crown of thorns etc etc.

If an intriguing Shroud  with an iconic double-image – front and rear – was helping to cement people’s wavering faith, then why not enhance the details?

If most, if not all the bloodstains on the Shroud were later additions, as I have previously argued (based on the Lirey pilgrim’s badge, circa 1355)  and the Lier copy, 1516 ) then there are practical problems that have to be addressed. The most pressing of them all is  finding a source of fresh blood before it has completely clotted (in the absence of anticoagulants such as heparin and citrate or other Ca-chelating agents). There are others too– like having blood that can be applied easily to linen, and which looks quickly authentic (red, but not too red, a little aged  etc).

This morning’s post addressed mainly the first item – coping with blood clots. So I floated the idea of freshly-drawn blood being placed into a pouch made of porous felt material, maybe with some soap as a wetting agent, AND – as a bonus – that same soap  assisting lysis (rupture) of the red cell membrane, thereby  releasing soluble haemoglobin that would then soak through the felt and attach to the linen in a predictable manner.

One idea invariably leads to another – which is what happened this morning. I got to thinking how blood might be obtained humanely, and thought immediately of the ancient practice of bloodletting, a routine procedure that involved nothing more than some shallow cuts with a lancet or other sharp edge.

I then recalled another way of drawing blood – one that has been around since time immemorial (pre-AD we are told)  – namely the use of blood-sucking leeches. I tossed that in for good measure.

Here I am a few hours later, having mugged up on leeches and their digestive systems, and suddenly I  find that it is the leech that, for me at any rate,  ticks lots of  boxes – or at any rate more boxes than a simple felt pouch. (In fact there’s no reason why they should not both be used together – a well-fed leech that has been macerated or otherwise divested of its last meal and then placed in a felt pouch – employed as a primitive felt-tip marker pen).

Let me explain. The leech has a prodigious appetite. It can take in 5 or 10ml of blood at a single sitting (and it’s said you will not feel its incision).

The leech stores a lot of blood – for months while it slowly digests the globin proteins…

It can then take the leech MONTHS to fully digest the blood, and the details of that digestion are fascinating (at least for the non-squeamish seeker after truth). Firstly, it would seem that the leech is only interested (primarily) in some of the proteins, notably the globin of haemoglobin. It is not interested in the serum – in fact it rapidly excretes the serum to its outside as a yellow slime. Why would it do that, one might ask – why waste good protein? The answer seems to be that the serum takes up too much space relative to red blood cells. The latter have much less water, so the leech excretes serum so as to pack in more red blood cells.

So the gut contents should be pasty rather than a runny liquid. I have long suspected from looking at Shroud Scope images that that blood looked too dry and caked-on to be real regular blood – confined as it is to the ribs of the weave with minimal bleed of faint pinkish-purple pigment into the deeper layers. I have also puzzled why there are areas where blood appears to have flaked off – leaving those pinkish areas as the only remnant. Why should real blood do that if, as claimed by Adler, it is not whole blood but a serum exudate with no blood cells and presumably highly diluted haemoglobin. However, if the contents of a leech gut are serum-depleted blood, with an enhanced  concentration of red blood cells with their membrane progressively degraded to release haemoglobin as a “sludge” – then the dabbed-on appearance of Shroud blood image can be rationalized. The blood was a semi-digested paste, with the stiff consistency, say, of oil paint rather than water-colour, with a greater propensity to stay where applied, and a reduced tendency to migrate in all directions.  (OK, so bloodstains are visible on the reverse side of the cloth we are told – or at any rate, some blood stains – but until those pictures are in the public domain I cannot comment).

Now here’s another fascinating detail: the leech is only interested in the haemoglobin protein. Once it has digested that, it excretes the haem as iron and as porphyrin. So there’s no reason to suppose that ingested blood will quickly lose its red colour. Oh, and there’s another detail: the leech secretes anticoagulants when it sucks blood – for obvious reasons – to prevent blood from clotting.

Already one can see advantages in using the contents of blood-fed leeches. First the blood will be free of clots. Second it may have an aged look about it, but still be recognizable as blood.

There are some more subtle aspects too that are worth noting. With blood being the sole source of nutrition for the leech, it will be grateful for the physiological ions that come with it – notably potassium etc. The bloodstains on the Shroud are curiously deficient in potassium as Adler noted.  Leeches also harbour bacteria which are symbiotic, aiding the digestion of blood. It is possible that those bacteria modify the porphyrin of haem (protoporphyrin IX to be precise). Adler (again) discovered that the porphyrin of Shroud blood had an atypical spectrum. He attempted to account for it by invoking a complex with bilirubin – not his finest hour in my view – which is not to deny him credit as a thorough documenter of the facts. Might blood that has been through the long slow digestive processes inside a leech match the spectral changes that Adler observed – to say nothing of losing most of its potassium to leech “tissue”?

Even without all these biochemical subtleties, leeches have to tick a big box from the perspective of monkly convenience. First there are probably leeches available in the monastery as a standby remedy. So one does not have to draw blood on the day, and rush to use it before it has clotted. One uses the contents of a leech gut – always there when you need it. Secondly there are well-fed leeches that have blood inside them that is weeks or months old, and which is UNCLOTTED. Thirdly that blood, regardless of its degree of digestion, will always be red, but maybe not resembling fresh blood too closely. There maybe other advantages in using leeches too – maybe the “bloodstains” from a leech have better keeping properties that fresh blood from a human. Maybe all its accompanying bacteria, biochemical preservatives etc allow it to retain its appearance on one’s enhanced Shroud for decades, centuries even rather than weeks or months.

Once in a while a scientist (or in this case a retired one) has to play his hunches and stick his head above the parapet. I think the bloodstains on the Shroud were derived from leeches that had been fed on human blood, rather than fresh blood straight from the veins of a blood donor. Leeches represented good medieval biotechnology. Leeches were deployed in the service of spreading the Word – turning a Shroud with a scorched-on  image of a naked man with no apparent wounds into the strategically- bloodied and then most revered holy icon in the Western world.

Yes, the Shroud is almost certainly of medieval origin – but imprinting the image AND the bloodstains did not happen in a single step. The Shroud we see today was almost certainly the product of accretions over decades, probably centuries. It stands as a monument to human inventiveness – driven by religious fervour that was probably well-meaning, at least according to the religious mores and ethical standards of the times.

Colin Berry (aka sciencebod) PhD

Previously Head of Nutrition and Food Safety at the Flour Milling and Baking Research Association, Chorleywood, UK.


Background stuff:

“Wall paintings dating from 1400 B.C. depict the use of leeches for drawing blood from human beings.”

“Digestion of the blood meal is made possible by the presence of bacterial symbiotes, Aeromonas hydrophila and Pseudomonas hirudinis living in the digestive tract of the annelid. In the days following the blood meal, the blood contained in the diverticula of the stomach is concentrated by around 40% by the excretory system. The blood then undergoes very slow changes, in particular by progressive lysis of the erythrocytes involving 2 successive mechanisms: haemolysis and proteolysis. The haemoglobin is split into globin and haem; the globin is used by the leech’s metabolism and the haem is split into excreted iron and protoporphyrin. The digestion progress is extremely slow and takes several months. Once sated, leeches do not bite.

In the natural environment, access to prey is not always regular but the method of digestion of leeches makes them adapted to this lifestyle since they present an extraordinary resistance to fasting, being capable of fasting for 6 to 8 months at a time. Some leeches can even survive a fasting period of 18 months.”


Leeches excrete the plasma from their ingested blood meals. Excretion is

activated during ingestion, which increases feeding efficiency by increasing the

proportion of blood cells in the ingestate. Excretion continues for 4-6 days

following ingestion, removing all the remaining plasma from the ingestate. Leech

ingestion comprises stereotyped muscular movements, secretion of saliva and

excretion of plasma.”


Postscript: the first comment on the ideas in this and the previous post appears from Paulette, a US science teacher as I recall, on The Other Site (where else)?

“But Yannick, dear scholarly friend, you know perfectly well that Colin Berry has addressed the bloodstain issue. Medieval monks used medieval Magic Markers (felt pens) from the firm of Leeches & More, Ltd. They waited 217 years after scorching the image with a hot brass statue produced by the Barbizon School of Post-Napoleonic Forensic Realism. The monks waited until Whizzo Scorch Remover was invented in order to fool future scientists into thinking there was no image beneath the bloodstains.  Of course most of the bloodstains were added by Barrie Schwortz and are copyrighted…”

As I’ve said before, the view, nay dogma,  that the bloodstains were imprinted before the body image arrived rests on  somewhat token and insubstantial evidence based on a single spot test with proteolytic enzyme on a microscope slide. I have to say that I am not in the least bit surprised that a STURP finding that provides a pro-authenticity answer should be instantly and uncritically accepted without anyone ever suggesting that independent confirmation is desirable by other workers using other methods. For my part I have used Shroud Scope to look closely at areas where there are both blood and body images. Not only do I see superimposition, but am fairly confident that where there is superimposition in patches where blood image has flaked away, leaving just a pinkish background, the body image (greyish on my adjusted contrast/brightness settings) is BENEATH the pink, not on top. If you had two rubber stamps, one with grey ink, one with pink, would you not be able to discern the order in which they had been applied by judging which colour was more or less superficial and dominant?

I strongly suspect, based on Shroud Scope, that  the body image arrived first, probably  as a thermal imprint (superficial scorch) and the blood arrived later. To those who say it was blood first, based purely on one spot test, I say this: while there is room for humour in science, friendly joshing included, and yes I did have a chuckle when reading  the above comment, there is no room for dogma.   I would expect a science teacher to understand that…


About Colin Berry

Retired science bod, previous research interests: phototherapy of neonatal jaundice, membrane influences on microsomal UDP-glucuronyltransferase, defective bilirubin and xenobiotic conjugation and hepatic excretion, dietary fibre and resistant starch.
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3 Responses to Did blood-sucking leeches help to establish – at least in some eyes – the ‘authenticity’ of the Shroud of Turin?

  1. Pingback: Did the bloodstains really precede image formation on the Shroud of Turin? « Shroud of Turin Blog

  2. Pingback: Today is the day the gloves come off.. | The Turin Shroud: medieval scorch? Separating the science from the pseudo-science…

  3. Pingback: Mr. Barrie Schwortz, President of STERA Inc: please stop proselytizing incomplete, narrative-driven so-called science. | The Turin Shroud: medieval scorch? Separating the science from the pseudo-science…

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