Forensic serology refers to the detection, identification,classification and study of various bodily fluids such as blood, semen, saliva, urine, vomit, fecal matter, perspiration( sweat ) for the purposes of legal matters. The detection begins with the presumptive test which gives the indication that specific bodily fluid may be present but the other confirmatory test confirms the presence of that particular body fluid. The confirmatory test confirms what actually that fluid is.
This is done for the identification purpose in criminal investigations. It holds the significance in criminal justice system as it links the crime with the criminal or excludes the involvement of any individual who is innocent.
It actually answers three questions:
A. what is the nature of biological evidence sample? (Identification )
B. what is the species origin of the sample ( whether human or animal origin)?
C. Who the biological evidence belongs to ( individualisation)?
The examination is done once the Biological evidence collected carefully from the crime scene. Let us take a quick look at the kind of biological fluids most commonly encountered at the scene of crime.
Blood is constantly circulating fluid which delivers the necessary substances such as nutrients, oxygen, hormones etc. It transports metabolic waste products away from the body such as carbon dioxide etc.
FUNCTION OF BLOOD
- Transporting medium for all substances
- Protection by exhibiting immune responses
- Coagulation by Clotting factor fibrin
- Acts as messenger by transporting hormones.
It consist of two major parts :
- Cellular part : this comprises RBCs ( Red Blood Cells ), WBCs ( White Blood Cells ), platelets
- Fluid parts : this comprises plasma.
The red colour of the blood is due to presence of a pigment called haemoglobin.
Note : To read more about the composition of blood , please go through this post on our website.
BLOOD AS A BIOLOGICAL EVIDENCE
Blood gives valuable information about what truly happened during the crime. Blood helps in proving association of a person to the crime scene. Sometimes blood also helps understand the time since death, manner in which crime occurred. Blood is mostly found in the violent cases,homicide, rape cases, hit and run accidents etc.
Semen is the fluid ejaculated by the male reproductive tract. It is also called seminal fluid.Semen is translucent with white, grey or even yellowish tint colour. The total volume of semen for each ejaculation of a human male averages between 2 and 5 ml.
It fascilitates the succesful fertilization as it is capable of fertilising female ovum.
It is composed of spermatozoa and seminal plasma. Spermatozoa is the male generative cell whereas the seminal plasma keeps the sperm cells viable.
Four glands contribute their secretions to the seminal fluid that are
- Seminal Vesicle,
- Prostate gland
- Bulbourethral gland.
SEMEN AS A BIOLOGICAL EVIDENCE
It is considered the most important type of evidence since it is very useful in the cases of sexual assault to prove that sexual or physical contact occurred. It can identify the perpetrator by further DNA analysis. It can be detected in the vagina of the victim or on the clothing , bed sheets etc.
Urine is the by product of the cellular metabolism in humans. It is produced by kidney and follows a pathway from kidney to urinary bladder by ureters and then finally excretes out by urethra. Its color varies from transparent to yellow. On an average urine production is around 1.4 Litres per day by a person.
- Elimination of waste from the body
- Controls the level of electrolytes and metabolites
- Regulates pH homeostasis of the blood
- Regulates blood pressure
It comprises majorly of water, urea, chlorides, sodium, potassium, creatinine,uric acid, ammonia, phosphates, sulphates.
Urine As A Biological Evidence
It can be found in the cases of Strangulation, violent cases, poisoning cases, sexual assault etc. It can be used to analyse the presence of drugs, proteins , alcohol and poisons. Urine is not much evidentiary for DNA analysis.
Saliva (referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. It is a complex fluid where the various constituents acts alone to perform different functions in the oral cavity.
- Acts as a lubricant
- Digestion of food
- Maintenance of oral hygiene
- Improves taste
- Maintains the pH of mouth
- 99% of water
- electrolytes such as sodium, potassium, calcium,magnesium, chloride, bicarbonate etc.
- enzymes such as α-amylase , lysozyme etc
SALIVA AS A BIOLOGICAL EVIDENCE
The identification of saliva stains may be important for criminal investigations. It can be found in the cases of poisoning, animal bites, sexual assault, drug or alcohol abuse. They can be present on a cigarette, any food stuff, handkerchief left at a crime scene. The victim of sexual assualt may have saliva stains on the body. It can be the source of DNA or can also identify the blood type.
SWEAT ( PERSPIRATION)
Sweat is the fluid secreted by the sweat glands also called sudoriferous glands which are exocrine glands.Maximum sweat rates of an adult can be up to 2–4 liters per hour or 10–14 liters per day.
- Regulates the levels of electrolytes
- majorly water
- trace amounts of lactic acid, and urea.
- minerals such as sodium, potassium, calcium, magnesium,copper, iron
SWEAT AS A BIOLOGICAL EVIDENCE
Sweat can be found in the cases of sexual assault, violent cases, drug or abuse cases. A criminal may often leave behind garments at the crime scene of his criminal activity. These garments may have perspiration stains. Their position will quite be clearly indicative of their origin. It may tell about any particular drug or disease as well.
Faecal matter are the solid or semisolid remains of food that could not be digested in the small intestine. Bacteria in the large intestine further break down the remains. it contain a relatively small amount of metabolic waste products such as bacterially altered bilirubin, and the dead epithelial cells from the lining of the gut
Feces are discharged through the anus or cloaca during defecation.
- excretes out as a waste product.
- 75% of water
- 25% of solid
- 30% of solid matter is indigestible food matter
- 10-20% is cholestrol
FAECAL MATTER AS A BIOLOGICAL EVIDENCE
The identification of faecal deposits on clothing occurs frequently in cases involving homosexuality or homosexual assaults. It may also be present at the crime scene because abnormal mental aberration of the perpetrator or simply because of nervousness or natural desire. It can be found on the footwear or clothing etc.