Forensic Biology: Blood, Hair, Fibers, and Body Fluids

Vocabulary practice flashcards covering forensic tests, identification, and characteristics of biological evidence including blood, bloodstains, hair, fibers, and semen.

Biological Evidence

Blood of human or animal origin, semen, saliva, urine, and skin tissue submitted for identification and characterization by genetic factors such as isoenzymes and DNA profiles, excluding samples submitted for drugs, alcohol, or poisons.

Blood

The circulating tissue of the body consisting of a highly complex mixture of cells, enzymes, proteins, and inorganic substances in a faintly alkaline fluid with a normal pH of $7.35\text{ to }7.45$, making up about $5\,\text{liters}$ and $7\text{--}8\%$ of body weight in an average adult.

Erythrocytes (Red Blood Cells)

The most abundant formed elements in the blood, produced in bone marrow, possessing a biconcave disc shape and containing hemoglobin to carry oxygen to cells.

Leukocytes (White Blood Cells)

Irregularly shaped immune cells larger than red blood cells that destroy infectious agents known as pathogens.

Thrombocytes (Platelets)

Irregularly shaped cell fragments carried in plasma that aggregate together during coagulation to seal wounds and prevent blood loss.

Blood Plasma

The yellowish liquid portion of blood comprising $55\%$ of total blood volume, composed of $90\%$ water and $10\%$ solids such as albumen, globulins, fibrinogens, electrolytes, nutrients, hormones, and antibodies.

Benzidine Test

A preliminary color test for blood that detects stains diluted to $1:300{,}000$ parts, yielding an intense blue color upon reaction with benzidine solution and $3\%$ hydrogen peroxide; discontinued due to being a known carcinogen.

Phenolphthalein Test

A preliminary blood test capable of detecting blood at dilutions up to $1:80{,}000{,}000$ parts, where a positive reaction produces a rose, deep pink, or permanganate color.

Guaiacum Test

A preliminary blood test utilizing tincture of guaiac resin and hydrogen peroxide or turpentine to detect fresh blood in dilutions of $1:50{,}000$, producing an immediate beautiful blue color.

Leucomalachite Green Test

A preliminary chemical test for blood using leucomalachite green dissolved in glacial acetic acid and hydrogen peroxide, developing a malachite green or bluish green color in a positive result.

Luminol Test

A highly sensitive presumptive test capable of screening large darkened areas for bloodstains diluted up to $10{,}000$ times by producing luminescence or emission of light without color.

Peroxidase Principle

The biochemical mechanism underlying the four preliminary color tests for blood, wherein peroxidase present in hemoglobin carries oxygen from hydrogen peroxide to active reagents to form colored oxidation products.

Teicmann Test (Haemin Crystal Test)

A confirmatory microcrystalline blood test using sodium chloride and glacial acetic acid under heat, which yields dark brown rhombic crystals of haemin or haematin chloride arranged singly or in clusters.

Acetone-Haemin Test

A confirmatory microchemical test for blood utilizing acetone and dilute acetic acid or oxalic acid to produce small dark, diachronic acicular crystals of acetone haemin.

Haemochromogen Crystal Test (Takayama Test)

A confirmatory microcrystalline test for hemoglobin using a reagent containing sodium hydroxide, pyridine, and glucose, which forms large salmon-pink rhombic crystals clustered in sheaves within $1\text{ to }6\,\text{minutes}$.

Spectroscopic Test for Blood

The most delicate and reliable confirmatory test for blood in both old and recent stains, using an optical spectroscope to observe characteristic dark absorption bands across the solar spectrum produced by specific hemoglobin derivatives.

Precipitin Test

A standard serological test used to distinguish human blood or protein from animal origin by layering a blood extract onto human antiserum, producing a white cloudy line or band at the liquid interface.

Agglutinogens

Inherited chemical structures or antigens located on the surface of red blood cells (classified as A and B) that stimulate agglutinin production and dictate ABO blood type.

Agglutinins

Antibody proteins found in blood plasma or serum (classified as anti-A and anti-B) that react with specific foreign antigens to cause agglutination or clumping of red blood cells.

Universal Donor

An individual belonging to blood group O who lacks A and B antigens on their red blood cells and can donate red cells to recipients of any ABO group.

Universal Receiver

An individual with blood group AB who possesses both A and B antigens on red blood cells and no plasma anti-A or anti-B antibodies, enabling them to receive blood of all ABO groups.

Locard Exchange Principle

The forensic tenet stating that whenever there is contact between two surfaces, an exchange of materials will occur.

Keratin

The primary structural protein composing hair as well as fingernails and toenails.

Hair Follicle

The skin structure that produces hair, which develops entirely during fetal development with no new follicles forming after birth.

Melanin

The brownish-black pigment chemical responsible for determining hair color based on its relative concentration.

Hair Cuticle

The outer protective coating of the hair shaft composed of overlapping scales.

Hair Cortex

The protein-rich intermediate and thickest layer of the hair shaft surrounding the medulla that contains the color pigments.

Hair Medulla

The central core canal running through a hair shaft, which may vary in thickness, opacity, continuity, or be entirely absent.

Medullary Index

The mathematical ratio of the diameter of the medulla to the overall diameter of the hair shaft, measuring $< 0.05$ in humans and certain monkeys and $> 0.05$ in almost all animals.

Fiber

The smallest unit of a textile material possessing a length many times greater than its diameter, capable of being spun into yarn and woven into fabric.

Natural Fibers

Textile fibers derived directly from plants or animals, such as cotton (most common plant fiber) and wool from sheep (most common animal fiber).

Synthetic Fibers

Man-made fibers that comprise more than half of all textile materials, exemplified by nylon, rayon, and polyester.

Semen

A viscid, faint yellow body fluid produced by males for fertilization with a characteristic odor, normal pH of $7.2\text{ to }7.8$, and immediate gel-like clotting properties.

Seminal Plasma

The protein-rich fluid comprising approximately $90\%$ of semen, secreted by the prostate gland and seminal vesicles, containing citric acid, ascorbic acid, fructose, zinc, and spermine.

Spermatozoa

The male gametes or sex cells produced in the testis, each possessing a pear-shaped head, short neck, and a tail approximately ten times the head length, comprising about $10\%$ of semen volume.

Aspermia

A medical condition characterized by a complete absence of spermatozoa in the seminal fluid.

Oligospermia

A condition characterized by an abnormally low sperm count or few spermatozoa in the ejaculate.

Hematospermia

The abnormal presence of blood within the semen.

Leucocytospermia

The abnormal presence of white blood cells within the semen.

Asthenospermia

A condition characterized by poor motility and reduced forward progression of spermatozoa in semen.

Necrospermia

A semen abnormality where there are no living or motile sperm present in the ejaculate.

Florence Test

A preliminary chemical test for seminal stains introduced by Dr. Florence of Lyons designed to detect choline.

Barberio's Test

A chemical test almost specific for human semen that detects the presence of spermine in fresh, dried, or dissolved stains up to six years old.

Acid Phosphatase Test

The best chemical method to locate and characterize seminal stains by identifying the enzyme acid phosphatase via the rapid development of a blue or purple color.

Spermato-precipitin Test

A biological serological test proposed by Farnum in 1901 used to distinguish human seminal fluid from animal seminal fluid, especially in cases of bestiality.