B is for Blood

Picture of Blood Analysis

photo credit: Jack Spades via photopin cc

It is time to mind your ABCs because it is Crime Fiction Alphabet (CFA) time. If you are unfamiliar with CFA, it is a challenge run by Kerrie over at Mysteries in Paradise, so head on there and sign up, or click on some links and read what others have to say. This is my second time at this rodeo, and I have chosen to focus on topics related to crime fiction rather than books and/or authors. So without further ado,

B is for Blood

I hope you had your dinner a while ago because if you don’t like blood, this could get queasy. But, if you’re a vampire, then this is your lucky day. Let’s start by getting the basics out of the way.

First, the etymology. According to the Oxford English Dictionary, the word “blood” dates to the oldest English, circa 1000 AD. The word is derived from Middle English, which is derived from the Old English word blôd, which is akin to the Old High German word bluot, meaning blood. The modern German word is (das) Blut.

Second, the biology. Blood is made up of 4 things – plasma (the liquid part of the blood) and the three kinds of cells – Red Blood Cells (the oxygen carriers), White Blood Cells (the infection fighters and, more importantly for crime fiction writers, where the DNA is found), and Platelets (which allows blood to clot). This is overly simplified and, of course, common knowledge to most of us but is worth repeating.

Now, for the most important part, the use of blood in criminology. In forensic medicine, the term blood residue is used to refer to the wet and dry remnants of blood. But before you can start analyzing blood residue, you have to find it. If you have watched an episode of CSI or any other forensic procedural, or read a book on the same topic, you know about Luminol – that stuff they spray on surfaces to detect blood residue. Luminol reacts to the iron found in hemoglobin and turns blue. The reaction lasts only about 30 seconds but even minute traces of iron is enough to cause the reaction. However, Luminol does have drawbacks – it responds to other compounds like those containing copper and certain bleaches. Cleaning with bleach doesn’t remove blood residue as much as disguise it enough that an accurate reading cannot be made. Horseradish sauce and poop also cause false-positives. Now imagine your murderer, cleaning up after himself by opening up a jar of horseradish sauce or, better still, taking the time to err… do his business, after he has done his business.

Once we have found the blood, it can help us solve crimes! Of course, everyone knows that blood residue gives us DNA (but only the white blood cells do that. Red blood cells do not have nuclei) that can help identify both victims and murderers. But blood can do much more. Properly done, it can tell you when the crime happened and where.

If you have read more than one Perry Mason novel, it is likely you have encountered the use of blood pooling in determining the time of death. When the heart stops beating, blood stops flowing and starts to settle (pool), and depending on a number of factors (like the temperature, body position etc), the settling of blood has a specific timeline that can be used to determine when death occurred  In addition, freshly dried bloodstains are reddish-brown in color. Over time, under sunlight and exposure to weather patterns, blood fades to a gray stain.

The second aspect of blood in forensic evidence is in bloodstain pattern analysis – or that thing that Marg Helgenberger and Michael C. Hall do in CSI and Dexter respectively. Spatter analysis can help the analyst determine where the event happened in 3-dimensional space – i.e., where and how high off the floor the victim was when the blow fell. They can do this because the shape of a stain is an ellipse, and the ratio of the major and minor axes of the ellipse (the width and length of the shape) is equal to the sine of the angle of impact of the droplet. Some trigonometry later, you can determine the angle at which the droplet traveled  If you have enough such droplets, you can construct their paths and find out where they converge. This convergence point is most likely where the event happened. Of course, the details are a little more complicated but the process is straightforward.

Even when the blood is still in the body, it can tell the analyst the state of the victim before he or she died. Bruising indicates areas of trauma that can point us to the cause of death. Analyzing the blood itself can also be helpful. Exposure to Carbon Monoxide causes blood to be bright red. In Cyanide poisoning, body is unable to absorb oxygen leading to increase redness of your venous blood (blood in your veins) .The specific list of blood tests and the poisons that can be detected with them is too long for this blog post but they are out there but hopefully the next time your victim keels over, you know some of the different ways you can make their death interesting and mysterious.

Trivia that may interest only me.

The jumping spider uses blood flow like a hydraulic pump,  forcing its blood into the legs under pressure causing the legs to straighten for a powerful jump, without the need for bulky muscles.

Bloodletting, while mostly a load of crock, can actually be used in the management of a few rare diseases, including Hemochromatosis and Polycythemia. If I remember correctly, there was an episode of House devoted to exactly this (After 8 seasons, I would be surprised if there wasn’t an episode of House devoted to some strange unheard of disease and/or cure).


9 responses »

  1. Margot Kinberg

    Peter – This is really, really interesting! And it’s an excellent way to go about this alphabet meme – innovative and informative. Thanks very much for the background.

    • Thanks Margot. I started off planning to write a few lines about blood but then I found myself getting sucked into wikipedia. I finally had to stop myself from reading through the 3 dozen webpages I had open and start writing.

  2. Wow, lots of information about blood and its use in crime detection here. I was vaguely aware of a lot of this from watching TV shows, as you mentioned, but the extra detail is fascinating. Great post.

    • Thanks Tracy. Reading up on blood was like going down the rabbit hole. It just kept going and going but it was very interesting.

  3. What a great post (and luckily I had my dinner about two hours ago….)! Now you’ve got me curious about what it is about horseradish sauce that interferes with blood analysis…..

    • Bev, Thanks. And I believe there are compounds in Horseradish that catalyze the same reaction that the iron in blood does which leads to the false-positive.

  4. Lots of interesting information about blood. It looks like a great idea to carry Horseradish sauce, you never know when you may need it.

  5. Another interesting topic.


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