The Science of Fingerprints: Classification and UsesUnited States. Federal Bureau of Investigation
Science
The Science of Fingerprints: Classification and Uses
United States. Federal Bureau of Investigation
Fingerprints
In many instances, where the ridge detail on the outer surface has
been destroyed or is not discernible, the ridge detail is clearly
visible on the underside (fig. 394). If this is the case, the skin is
inverted (turned inside out) very carefully to prevent splitting or
breaking and then is inked and printed in the usual way. It must be
borne in mind, however, that when the underside of the skin is printed
the resulting impression will be in reverse color and position; that
is, the ink is actually adhering to what would be furrows of the
pattern when viewed from the proper or outer side. If it is deemed
inadvisable to try to invert or turn the skin inside out for fear of
damaging it, a photograph of the inner ridge detail is made and the
negative is printed to give an "as is" position photograph for proper
classification and comparison purposes. In order to secure good
photographs of the ridge detail it may be advisable to trim the skin,
flatten it out between two pieces of glass, and photograph it in that
position (fig. 395).
When the entire finger is placed in the solution during the hardening
process, the skin, in absorbing the formalin solution, may swell and
come loose from the finger. Should this occur, the skin must be
removed carefully and the procedure outlined above followed. If,
however, the skin still adheres to the finger and is not too wrinkled,
ink is applied and prints made. Should the skin be too wrinkled to
secure a satisfactory impression, consideration is given to the
injection of the tissue builder under the skin as previously
mentioned, in order to distend the pattern area. If successful, the
finger is inked and printed. This, of course, can be done only when
the skin is intact.
Should part of the skin be destroyed to the extent that tissue builder
cannot be injected effectively, while examination discloses that the
pattern area is present but wrinkled, cut off the entire pattern area
from the joint to the tip of the finger (fig. 396). Care must be
exercised to insure getting the complete fingerprint pattern as well
as cutting deep enough to avoid injury to the skin.
[Illustration: 396]
After excision, the flesh is carefully and meticulously removed from
the inside by scraping, cutting, and trimming until only the skin
remains, or until the specimen is so thin it can be flattened out to
remove most of the wrinkles. If the skin is fairly pliable, the
operator should attempt to place it over one of his own fingers and
try several prints. If the prints secured are not suitable, the piece
of skin (exert care to avoid breaking or splitting) is flattened out
between two pieces of glass and photographed (figs. 397, 398, 399).
[Illustration: 397. Inked print made from the finger of deceased
before treatment.]
[Illustration: 398. Inked print made after skin was removed and
treated.]
[Illustration: 399. Photograph of ridge detail of skin flattened
between two pieces of glass.]
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