By Ruth Siddall, on 9 August 2016
This blog post is not for the squeamish, but it is about a pigment that everyone is familiar with, although many of us have probably never heard its name. In the response to the Pigment Timeline Project’s survey, Dr Lewis Griffin of UCL Computer Science, told us that he had recently conducted research concerned with the colour of babies’ stools. This was something we just could not ignore.
I interviewed Lewis about his research on the pigments responsible for the colour of human faeces and particularly those of neonatal babies. You will be relieved to find that this article will be light on images (readers of a sensitive disposition are discouraged from googling an image search of some of the more unfamiliar terms used below). And yes, the colour that will represent UCL Computer Science in the Pigment Timeline Project is sh … err, Stercobilin Brown!
Lewis is a Reader in Computational Vision. One of his specialities is colour vision; analysing human colour vision and perception and from this creating robust mathematical models which can be used in the design of image analysis equipment and applied in the quantification of colouring components in materials.
A dear friend who studied at Harvard University once told me that when at College Football matches against fellow Ivy League institution Brown University, the chant that rang out from the bleachers was ‘What’s the colour of sh*t? Brown! Brown! Brown!’ Why is excrement brown? It is largely down to the organic pigment stercobilin. Stercobilin is ultimately derived from haemoglobin, which makes red blood cells red. Red blood cells degenerate after ~ 120 days, producing heme. Heme is then transported to the liver where it is attacked by enzymes, which strip out the iron and convert it into greenish-coloured biliverdin. This is secreted into bile which passes into the gallbladder. Here it converts to bilirubin, which is yellow. Bilirubin is responsible for the yellow colouration of some gall stones. Bilirubin is secreted into the large intestine where bacteria break it down forming, ultimately brown compounds stercobilin and related compounds stercobilinogen and urobilin. These are the pigments which make excrement brown.
Now, we are all aware of how the colour of our excrement can be a proxy for health, diet, Guinness consumption etc., and let’s be honest, we all notice it. The failure of bilirubin to be excreted from the gall bladder can result in a number of medical conditions. People who have an especial interest in the excrement of others are new parents. Dr Griffin’s opening line of his recent paper in Color Research and Application reads ‘Many parents are surprised and fascinated by the stool colours of their firstborn.’ There’s a line to get your attention. I don’t have kids, but two of my close friends have had children in the last couple of months and I probed them on this. Gary told me he would not go so far as to use the word ‘fascinated’ (but you could tell he was), and Rachel demonstrated a high degree of newly learned literacy on the colour and significance of baby faeces. Lewis was absolutely right.
The colour of baby stools is important. A congenital liver disease called biliary atresia can occur in newborns, it may result in a neonatal liver transplant and is potentially fatal but it is treatable if detected early (see Bakshi al., 2012). It occurs when the bile duct is blocked, preventing bilirubin from entering the gut and ultimately preventing babies from fully digesting milk. Consequently, infants afflicted by this condition produce ‘clay’- or ‘putty’-coloured stools.
There is a well-recognised transition in the colour of (healthy) baby excrement. Newborns first pass almost black, tarry faeces, called the meconium (if you haven’t had a kid, and you don’t know what this looks like, don’t google images. Trust me). This is waste present in the baby’s bowel at birth, and is mainly amniotic fluid, bile and mucus. This is what comes out in the day or so after birth. Progressively the faeces turn from an olive green to a mustard or, if you are of an artistic temperament, yellow ochre. Normal, brown stools are passed at around 6 months of age. However, poorly digested milk can produce pale, putty-coloured stools, an indicator of potential biliary artesia. Therefore it is really important that doctors and parents can readily identify stool colour as ‘healthy’ or ‘suspect’. Lewis and colleagues’ work with medical staff has showed in a trial, that one third of stools were not correctly identified (Bakshi et al, 2012). These are children who could have gone on to be seriously poorly. How can this hit rate be improved?
Lewis’s team measured the colour of 148 stools from healthy babies. The things we do for research. The first step was to observe and measure the range of stool colours under tungsten light using a spectroradiometer. This device can quantify the colour observed in refelected light. Griffin et al. (2015) then simplified the colour of infant stools into three components ‘Dark’, ‘Pale’ and ‘Yellow’ (D, P, Y), they tentatively identified these colours with pigments; D being meconium and unreacted bilirubin; P as partially digested milk fats and Y as being our friends stercobilinogen, stercobilin and urobilin. The colour of stools could now be plotted as mixtures of these three end-members and the colours observed recorded as Munsell coordinates (below). These colours may be regarded as the range exhibited in the stools of healthy babies.
The whole point of this study was to begin to design a simple process whereby doctors or parents could assess a baby’s health from a non-technical observation of the baby’s stools and without the need of a lifetime’s research in computational colour analysis. In Japan and Taiwan, simple stool-colour charts are used to help identify unhealthy babies and have been found to be very effective. The UK Children’s Liver Disease Foundation (CLDF) produce a similar card and a handy stool-colour bookmark, in the hope that these will be used routinely; at present they are not, and yet this is a simple and intuitive visual test that requires little training. The CLDF have also recently produced a Yellow Alert app for health visitors
Lewis’s research is still a work in progress with only the stools of healthy babies studied at present. However it shows how important colour and colour perception are in diagnosing potentially fatal diseases, and this colour is most welcome on The Pigment Timeline.
As a coda, you may be surprised (or horrified) to learn that a number of artists have looked to stercobilin and related pigments to create works of art, and there are references to it occurring in some of the most obscure historical artists’ palettes. After all, it’s cheap and easy to obtain. Several artists have (allegedly) used their own and others’ excrement in their art work; famously (and controversially) Andres Serrano and Piero Manzoni. More recently Chris Ofili hit the papers for using elephant dung as a pigment. And then there’s this.
Manzoni produced 90 cans of his own excrement (in a numbered edition, obviously), produced and tinned in 1961. His statement here was about intimacy to the artist, something real, tangible and confidential; ‘if collectors want something intimate, really personal to the artist, there’s the artist’s own shit, that is really his’ he wrote to his friend and fellow artist Ben Vautier in December 1961 (Battini & Palazzoli, 1991). It is not said what Vautier’s response was or whether he forked out for a tin. However there is one in Tate Britain (below, left). This work and similarly Serrano’s ‘Piss Christ’ depicting a photograph of a crucifix suspended in a jar of the artist’s urine are extremely controversial not only in their subject matter but also in the fact that NO ONE IS REALLY SURE IF FAECES AND URINE IS WHAT WAS REALLY USED. It is left to our imagination to conjure up the worst or the best case scenario with these artworks.
I have never been minded or, indeed, asked to analyse a work of art containing stercobilin and related compounds as a pigment. Please note, that I am *NOT* looking for donations to my pigment reference collection just yet. However, bilirubin has been used and gets a mention in The Pigment Compendium under ‘Gallstone’. Bilirubin-based yellow and brown pigments were created historically from gallstones and gall bladders; there are references from the 3rd Century AD Greece to grinding fish galls with chalk and vinegar to produce faux orpiment. The ‘Gaule of Eeles’ was used similarly during the Medieval period … and then it was all ox gallstones and gall bladders in the 16th Century. Anyway I digress. Bilirubin looks quite pretty under the microscope. I’m grateful for the University of Cornell’s School of Veterinary Medicine‘s online spotter’s guide to particles in urine for the image below.
I don’t have a picture of stercobilin. This may be a good thing.
Bakshi B., Sutcliffe A., Akindolie M., Vadamalayan B., John S., Arkley C., Griffin L. D. and Baker A. (2012). How reliably can paediatric professional identify pale stool from cholestatic newborns?, Archives of Diseases in Childhood, 97(5):385-387.
Battino, F. & Palazzoli, L., 1991, Piero Manzoni: Catalogue raisonné, catalogue no. 1053/4., Milan, 472-5.
Cornell University of Veterinary Medicine; http://www.eclinpath.com/urinalysis/crystals/bilirubin-2/
Eastaugh, N., Walsh, V., Chaplin, T., & Siddall, R., 2008, Pigment Compendium: A Dictionary and Optical Microscopy of Historic Pigments. (1st ed.). London: Butterworth-Heinemann., 958 pp.
Griffin L. D., Sutcliffe A., Bradbury K., Kumble S., Mylonas D. and Baker A. (2015). Colour and spectral reflectance of stools from normal neonatal babies., Color Research & Application, 40(6):585-591.
Griffin Lab http://imageanalysis.cs.ucl.ac.uk/index.php
Nazer, H. and Roy, P. K., 2016, Unconjugated Hyperbilirubinemia., Medscape., http://emedicine.medscape.com/article/178841-overview#showall
Piero Manzoni; Artist’s Shit, 1961, Tate Britain: http://www.tate.org.uk/art/artworks/manzoni-artists-shit-t07667