Latent Fingerprints

The latent fingermark, deposited by the fingertip pattern, is a complex mixture of natural secretions and contaminations from the environment. Three types of glands are responsible for the natural secretions of the skin, the sudoriferous eccrine and apocrine glands, and the sebaceous glands. The sudoriferous glands are distributed all over the body and produce the sweat. The secretory body of each gland is formed of a long coiled tube situated in the subcutaneous layers of the skin. The glands transverse the epidermal layers to open at the summits of the papillary ridges to form ‘sweat’ or sudoriferous pores. Sweat is an aqueous solution produced by the cells of the secretory body, without loss of cell cytoplasm for the eccrine glands in contrast with apocrine glands – this explains the difference in chemical composition between these two types of secretion. Eccrine sweat is approximately 98.5 per cent water, the remainder being principally made up of mineral salts, eg, sodium chloride, organic acids, urea and sugars.

The palms of the hands and the soles of the feet produce only eccrine gland secretions, whereas the apocrine glands are located in the groin, in the arm pits, and in the perianal regions, where they generally open at the hair follicles.

The sebaceous glands are found on the chest and the back, where they are associated with hair roots, and on the forehead, the lips of the vagina, the glans of the penis, and the mammary areolae. These glands secrete an oil, the sebum, which serves to protect the skin and hair against water, to act as a lubricant, and also to help absorb fat, lipid, soluble substances. The fatty substances secreted by the sebaceous glands are not water-soluble.

These three types of glands, therefore, have well defined functions and the chemical composition of their secretions vary in consequence.

The major chemical constituents of the glandular secretions

CONSTITUENTS

SOURCE

INORGANIC

ORGANIC

eccrine glands chlorides
metal ions
sulfates
phosphates
ammonia
water (>98%)
amino acids
urea
uric acid
lactic acid
sugars
creatinine
choline
apocrine glands iron
water
proteins
carbohydrates
sterols
sebaceous glands fatty acids
glycerides
hydrocarbons
alcohols

As the ridges of the hands are covered exclusively by eccrine glands, eccrine gland secretions are present to some degree in every latent fingerprint. Contamination by sebaceous gland secretions is also very common, whereas that from the apocrine glands is much rarer but may be important in certain crimes, eg, crimes of a sexual nature.
Sebaceous material is often transferred onto the hands by contact between the hand and the forehead, the nose and the eye region of the head. This is encouraged unwittingly by irritation, by common postures when sitting, eg, rubbing the forehead, and by other natural everyday occurrences, such as combing the hair.

Latent fingermarks can be of the type discussed above, where materials emanating from the human body are the basic for the chemical composition of the latent print. However, contaminants from the workplace which dirty the hands are also valuable when detecting latent prints. Blood is an agent that abounds at the scene of certain crimes of violence and can sometimes be the major contaminant which provides the print. Where the print deposit is heavy, it can be detected visibly, for lighter prints, enhancement can normally be achieved by the application of blood staining reagents.

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