Vomit As A Forensic Evidence

Vomiting is the involuntary, forceful expulsion of the contents of one’s stomach through the mouth and sometimes the nose. Emesis is the medical term for vomiting.

Receptors on the floor of the fourth ventricle of the brain represent a chemo-receptor trigger zone, known as the area postrema, stimulation of which can lead to vomiting. Vomiting after eating usually expels the contents of the stomach and therefore the undigested contents of the meal. Matter from the stomach that has come up into and may be ejected beyond the mouth, due to the act of vomiting is known as Vomitus.

FEATURES OF VOMITING

• pH  : the pH of the vomitus is almost always highly acidic.
• Odour : foul smell
• Colour : Sometimes the vomitus may be streaked in blood and be a red and brown colour. This is called blood vomiting or hematemesis.
  Fresh blood in the vomit appears red and usually comes from the upper gastrointestinal tract.
  Blood that comes from the lower gastrointestinal tract usually undergoes oxidation and may appear brown in color.
  Clotted blood appears dark red in color and is usually seen when there is perforation of a peptic ulcer.
  Contractions of the duodenum lead to the secretion of bile in the vomitus. This gives a greenish tinge to the vomit. Severe vomiting may often yield green coloured vomit, although a bile-containing vomitus may also be yellow in colour.
  

EXAMINATION OF VOMIT

For the examination of vomit, presence of the following materials are to be taken into account:

1. Presence of Mucus
2. Free HCl
3. Endothelial cells from gastric mucosa
4. Undigested and semi digested food material

A.Test for Mucus

• To the extract add 33% acetic acid drop by drop.
• Opalescence appears which may be due to mucus or lipoid substance or both.
• If on addition of more acetic acid opalescent does not disappear, presence of mucus is confirmed, because with excess of acetic acid lipoid globulins dissolve but not the mucus.

B.Test for Free HCl (Gunzberg’s Test)

• The reagent is prepared by 6 drops of 10% phloroglucinol in alcohol with 3 drops 10% vanillin in alcohol.
• In a porcelain evaporating dish one drop of suspected extract is placed and 1-2 drops of Gunzberg’s reagent is mixed at once.
• The contents are allowed to dry completely. A brilliant red colour indicates free HCl.

C.Endothelial Cells

 After centrifuging the extract for 10 minutes a thin film is made on a slide. The Endothelial Cells are observed under microscope.

D. Pepsin Assay Using a Fibrin Blue-Agarose Gel Plate

The pepsin within the sample is assayed for its proteolytic activity which is revealed in a fibrin blue-agarose gel plate, as a result of an enzymatic reactivity that takes the form of a concentric, blue, translucent ring around the tested sample. Apart from being able to determine the pepsin content of fresh or recent forensic samples, this method has also achieved positive reactions in aged gastric fluid stains that were kept at room temperature. No body fluids other than the gastric fluid and no proteolytic enzymes other than pepsin show a positive reaction with the use of this method. (Reference paper)

E. ELISA Detection of Gastric Mucosa-Expressing Proteins

four gastric mucosa-expressing proteins, pepsinogen I (PGA), pepsinogen II (PGC), gastrin (GAST), and mucin 5AC (MUC5AC) are used to detect the presence of vomit. Enzyme-linked immunosorbent assay (ELISA) procedure is used for the detection of these four candidate proteins. (Reference paper)

FORENSIC IMPORTANCE

The identification of vomit stains may be helpful for crime scene reconstruction. Vomitus can be found in the cases of poisoning or drug abuse,hanging or sexual abuse. The questioned sample could be tested for the presence or absence of any particular drug or poison if administered. This evidence is very rarely found at the crime scene and is not much evidentiary.