Storytellersunplugged

After about 16 more weeks, the growths would fuse together to form
sinuous structures that would enhance the grasping ability of the
creature.  Within about 12 more weeks, the creature would leave its
primal hideaway.  But its development would not stop.  It would continue
until the creature was four times its present length and more than ten
times its present weight.

It would no longer be called a fetus but would be called John Doe.  The
structures John developed are known as papillary ridges, as friction
ridges or, more commonly, as fingerprints.  The openings in them are
known as pores, and the glands, as sweat glands.  John Doe would mature
and ultimately be placed on trial for first degree murder in a
capital-punishment state.  It is at this point that his life would
depend on those little ridges.

According to many sources, fingerprints fall into four categories:
inked, plastic, patent or latent.  Inked prints are known, controlled
prints that are pressed onto what is known as a ten-card under the
supervision of a law enforcement officer or technician.  Plastic prints
are fingerprint impressions made in impressionable materials that retain
the shapes of friction ridges.  Such materials might include grease on
an automobile part, putty from a window frame, modeling clay and the
like.  Patent prints, also known as visible prints, are fingerprint
impressions formed by a transfer of some foreign matter, such as blood,
onto a surface.  Such impressions are visible and can be readily
photographed.  In the field of dactylography (the study of fingerprints
as a means of identification), latent prints are impressions, visible or
not, left by accident.  If you find the word dactylography difficult to
remember, note that it was originally named icnofalangometria.

According to an FBI publication, latent prints might be difficult to
see but can be rendered visible; and any print left at a crime scene on
almost any surface, sometimes even human skin, is referred to as a
latent print.  Such fingerprints can be made visible by such techniques
as using various colored powders to color ridge impressions so that they
contrast with the color of the surface bearing them.  Lasers and other
light sources are also used.  Another technique is glue fuming, in which
some glue vapors adhere to amino acids in a print.  I described this
process in some detail in my December essay, Lasting Impressions.  In
iodine fuming, iodine reacts with any oils and fatty deposits in latent
prints and forms an image that lasts long enough to be photographed.
Some fingerprints can also be recovered by using lifting tape, gel
lifters and flap lifters.

Speaking of the FBI, its Identification Division was created in 1924
with more than 800,000 fingerprint files, most of which were supplied by
the Levenworth Penitentiary.  The aforementioned FBI publication lists
its current number of fingerprint records at more than 250 million, and
it is increasing at a rate of 34,000 per day.  If all the fingerprint
cards were stacked, the pile would be higher than 133 Empire State
Buildings.  The print records have been computerized, and a list of
prints that closely match prints being compared can be quickly prepared
for a detailed comparison by trained technicians.

Contrary to popular thought, fingerprints are not normally oily.
Eccrine sweat glands are distributed over much of the surfaces of a
body, but they are especially abundant on the palms of hands, the soles
of feet and the forehead.  Such glands are one of four types of human
sweat glands; and they secrete a fluid containing many substances,
including acids, through pores in the fingerprint ridges but do not
secrete oils.  The fluid, or sweat, is used to control body temperature
by evaporation.

The major value of fingerprints is the fact that they are unique.  No
two prints have been found to be exactly the same, even those of
identical twins, who have the same DNA.  Also, unless they are
mechanically or chemically assaulted, most fingerprints can last for
several days, some for many years.  Plastic prints can last almost
indefinitely.  Since so many things, such as evaporation, oxidation,
absorption, dust, heat, cold, rain, humidity, cleaning, etc. can
deteriorate fingerprints, their age can usually not be determined.  Of
course, if a glass was washed two days before, prints found on it could
be assumed to have been left during those two days.

Fingerprint ridges come in three basic patterns: loops, which account
for 60-70 percent of patterns encountered, whorls, which account for
25-35 percent, and arches, which account for only about 5 percent.  Of
course, there are also subgroups.  For example, there are radial loops
that slant toward the thumb and ulnar loops that slant away from the
thumb.  The words radial and ulnar refer to bones in the forearm.  There
are plain whorls, accidental whorls, double loop whorls and central
pocket loop whirls.   There are also plain arches and tented arches,
depending on their shapes.   These terms describe specific ridge
configurations that would be difficult to describe without accompanying
illustrations.

In fingerprint analysis, there are three levels of detail.  The first
level involves general ridge flow and patterns they form.  These details
are insufficient to identify an individual but are sufficient to exclude
suspects.  Second-level analysis can identify an individual.  Depending
on which source is consulted, an average fingerprint reportedly contains
as many as 175 or even 300 individual ridge characteristics; but a
typical partial print found at a crime scene might contain only about a
fifth as many as a full print.  Second-level ridge features include a
termination, which is an end of a ridge; a bifurcation, which is formed
where one ridge splits into two ridges; a lake, which is formed where a
ridge splits and then rejoins; an independent ridge, which is a short
ridge; a point or island, which is a very short ridge; a spur, which is
formed where a short ridge leads away from another ridge for a short
distance; a crossover, which is formed where a ridge crosses from one
ridge to another; and a delta, which is formed between three joined
ridges.  Third-level detail gets really picky.  It takes note of
individual ridges’ dimensions, shapes, pores and edge configurations
and also other permanent details such as skin creases and scars. 

A common method for fingerprint  analysis involves a procedure known as
ACE-V.  It involves four steps.  Analysis is the first step, which is to
quantitatively and qualitatively assess all three levels of detail and
their ability to identify an individual.  Comparison is the second step,
which is to compare the various ridge attributes of one fingerprint
impression with another impression.  Evaluation is the third step, which
appraises the comparison to determine if there is sufficient detail to
draw a definite conclusion.  Verification is the fourth step, which
includes an independent analysis, comparison and evaluation of the ridge
impressions by another qualified examiner.

NEW TECHNOLOGY:

There is a new technique being developed for visualizing fingerprints
on metallic and electrically conductive surfaces without even touching
the print or surface.  And this can often be done after the surface has
been wiped with a tissue or heated to some 600 degrees Celsius.  Even
curved surfaces such as the surfaces of shell casings can be scanned.
The technique uses an instrument known as a scanning Kelvin probe (SKP).
 

Inorganic salts in sweat from finger ridges cause an electrochemical
reaction with a metal surface.  The reaction involves a formation of
metal-ion complexes, and these are not easy to remove.  In techno speak,
the salts depassivate the metal surface, which produces measurable
voltage differences between one point and another.  The probe measures
the voltage differences at preset intervals from small distances above
the surface.  An image of a fingerprint can then be produced by mapping
the measurements.  Resolution can be increased by simply measuring more
points in a given area, but sampling some 20 points per millimeter
provides enough detail for the purpose of identification.  Since prints
are not touched, material that might be used to obtain a DNA sample is
not disturbed.

AFTER WORD:

For those who are curious about the remaining three of the four types
of sweat glands mentioned, the second type is an apocrine gland.  These
secrete sweat containing fatty materials.  They are placed in certain
areas of a body; and bacteria breaking down organic compounds in the
sweat creates odors, thus enabling these glands to serve as scent
glands.  The third type of sweat gland is a ceruminous gland, and it
produces a type of modified sweat commonly known as ear wax.  The fourth
type of sweat gland is a mammary gland, and it produces a type of
modified sweat commonly known as milk.

A FEW EXTRA FACTS:

Callouses do not change the configuration of fingerprints.  The tough
outer layer of skin is constructed using the same cell structure as the
one below it.

John Dillinger had his fingerprints removed with acid, but his ridge
patterns reappeared.  Robert Phillips had his very fingertips surgically
replaced with skin from his chest.  Even that failed to protect him.  He
was easily identified by the ridges on the second phalanges of his
fingers.

Reportedly, a Roman attorney showed that a palm print was used to frame
someone for murder.  This took place …  nearly 2,000 years ago.