Nature of Blood and Presumptive Tests

Nature of Blood

• Blood is a specialized circulating tissue made of cells, enzymes, proteins, and inorganic substances in a fluid medium.
• Blood volume constitutes about 8% of body weight: approximately 5-6 liters in males and 4-5 liters in females.
• Blood components include:
  • Plasma (55%): the fluid portion mainly composed of water, enzymes, and glucose.
  • Cells (45%): consist of red blood cells (RBC), white blood cells (WBC), and platelets.
    • RBCs: transport respiratory gases; contain hemoglobin, giving blood its red color.
    • WBCs: responsible for immune defense against diseases.
    • Platelets: cell fragments crucial for blood clotting.
• Loss of 40% blood volume can lead to irreversible shock; 1.5 liters loss causes incapacitation.
• Clotting occurs when fibrin in plasma traps red blood cells, forming a solid clot separating serum.
• Blood type AB indicates mixed ancestry, consisting of A and B types.

Presumptive Tests for Blood

• Benzidine Test: Blue coloration indicates the presence of peroxidase enzyme in blood.
• Kastle-Meyer Test: Involves ethanol and phenolphthalein; violet color results from alcohol solvent reacting with hemoglobin.
• Guaiacum Test: Detects blood through blue coloration; less effective on older stains.
• Hemastix: Test strips become color bands when in contact with blood.
• Luminol Test: Produces bright blue color under UV light, indicating blood presence.
• Leucomalachite Green Test: Oxidation gives peacock blue color; less sensitive than benzidine test.

Microcrystalline Tests

• Teichmann Test: Evaporation of salt and acetic acid yields reddish-brown hemin crystals.
• Takayama Test: Addition of Takayama reagent results in large rhombic crystals with salmon color.
• Acetone-Haemin Test: Formation of small dark dichroic crystals.

Confirmatory Tests for Blood

• Stains on clothing should be air-dried, avoiding sunlight, and wrapped in paper for preservation.
• Soil exhibits the same care as other samples; store in glass containers or new paint cans, maintaining chain of custody.

Forensic Characterization of Semen

• Semen is viscous and gelatinous, becoming more liquid over time due to enzymes.
• Normal ejaculation volume ranges 1.5 to 3.5 ml, containing spermatozoa, epithelial cells, choline, and lecithin; slightly alkaline.
• The healthy male produces approximately 400 to 500 million sperm per ejaculation.
• Sperm conditions include aspermia (absence of sperm) and oligospermia (low sperm count).

Examination of Semen and Seminal Stains

• Physical Examination:
  • Microscopic examination stains sperm cells for observation under high power.
  • Ultraviolet examination reveals bright bluish fluorescence in seminal stains.
• Chemical Examination:
  • Florence Test: Tests for choline by forming dark brown rhombic crystals; limited by specimen handling and blood contamination.
  • Barberios Test: Identifies spermine picrate via slender yellow rhombic needles.

Forensic Entomology

• Medico-legal forensic entomology involves insects in crime investigations, including murder, suicide, and physical abuse.
  • It assesses insect activity on bodies to estimate time of death (postmortem interval) and location.

History of Forensic Entomology

• Sung Tz’u (1235 AD): Early death investigator noted for using insect behavior to solve a murder case.
• The case described involved flies being attracted to sickles, leading to a confession.
• Importance of necrophagous insects in determining crime scene details was highlighted.