The identification of the blood through the years
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When we talk about blood, alot of people might be quick to say it is a heterogeneous mixture without a proper definition or full meaning. The heterogeneity is well known, but how was blood identified in ages past? I think that is something to look out for in this post. Let's go there!
Firstly, let me try to massacre the blood in definitions. The blood is a crucial connective tissue I like to call the transporter. It is very important in every human. I call it the transporter because it carries along oxygen, nutrient and waste materials when circulating through the body. The reason it is called an heterogeneous mixture is because of the presence of different components like the red blood cells, white blood cells, platelets and plasma. The red blood cells being the majority has a component called the haemoglobin. The haemoglobin has an iron pigment known as heme and a protein known as globin. I think I don't need to tell you the reason behind the name....
Back in the 1900s, bloodstains at crime scenes such as rape, assault, homicide and the likes were not identified or lemme say they were seen just as mere stain. Since thme, until now, forensic serologists couldn't identify a criminal of a crime scene with the blood stain. But that's all a story now as a criminal can be caught with the slightest blood stain on the crime scene.
After collecting the stain, the forensics try to discern if it's a 1. blood stain or not 2. If yes, human or animal blood and 3. If it can be traced to any individual or not? In trying to identify the blood, two tests are done, the presumptive and the confirmatory test. The presumptive being not specific for blood and the confirmatory being specific for blood species:
- Presumptive test
This is the first step and it is also called the chemical screening test. It is used to determine of the stain on crime scene is blood or just a stain in a situation where it is dried. Some of the chemicals used by the forensics include phenolphtalein in 1901, leucomalachite green in 1904, benzidine in 1904 as well and lumino in 1928. But the use of benzidine was discontinued later because it was found to be a carcinogen. Allow me to references the next few sentences as they might be found on other pages...
The first step is to moisten a white filter paper with a distilled water. Apply the filter paper to the suspected blood stain. A portion of the stain will transfer onto the moistened paper. Then, you add the leucomalachite green reagent to the paper. The second step is to add hydrogen peroxide to the filter paper and look for a color change on the paper. A positive result will yeild a bluish-green color. When phenolphthalein is mixed with a dried bloodstain, with the addition of hydrogen peroxide, the hemoglobin in the blood causes the formation of a deep pink color.
The phenolphtalein and hydrogen peroxide added to the dry bloodstain triggered the haemoglobin to form a deep pink colour.
- Confirmatory Test
This is the second step in blood identification and as I said earlier, it is specific. They are usually specific for the iron pigment in the haemoglobin. Usually, a positive confirmatory result is shown by the presence of blood in the dry stain collected from ctime scene. The available confirmatory tests are: Ring precipitin test, the gel diffusion method, the microcrystalline test,the tiechmann test (1853), the takayama test (1905) and the electrophoresis(1907). The confirmatory test is used based on the fact that the iron pigment in haemoglobin(heme) will produce crystals of certain chemicals present during the test and these crystals can be detected on the microscope.
Well, it's good to know that the blood is composed of a lot of inherited factors called genetic markers and the determination of these factors is called blood groupin or typing. As much as the human beings are, it is very difficult to believe that no two humans will have the same combination of genetic markers but this is so true.
Dr. Karl Landsteiner announced human blood typing in 1900, a major discovery of the 20th century. His work brought out the ABO blood grouping system. Discoveries show that bloodstains can be typed in the ABO blood grouping system. What does this mean? It means the nabbing of criminals. The typing can be done in two ways:
1. Detection of the antibodies of the serum
This is the ancient method. In 1913, Lattes used this method in Italy although the procedure has now been modified. This test detects antibodies present in a dried bloodstain. The bloodstain is splited into two onto two microscope slides. They are now called type A red cells and Type B red cells(remember they are on either sides of the microscope). Everything is ready,
NOTE: This is a sensitive information and might be on other websites.
If the bloodstain on the slide contains anti-A antibodies, the A red cells that were added will agglutinate, which looks like crosslinked cells under the microscope. Agglutination of the A cells indicates that anti-A is present, and therefore, that the bloodstain is of blood group B.
2. Detection of the antigens of the red blood cells
This type of blood typing takes advantage of the fact that the antigens remain present in dried blood stain even after the blood cells break apart. This approach thereby finds it easy to detect the antigens on the surface of the red blood cells. The two main exhibition methods include:
Absorption- inhibition
This method estimates the amount of antibodies present in an antiserum before and after exposure to a stain extract possibly containing an antigene.
Absorption-elution
"The absorption-elution method is based on the theory that blood-group antibodies can bind to their specific redcell surface antigens in bloodstains. The antigen-antibody complex can then be dissociated and the antibodies recovered"
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