Wounds to the vulva are dangerous, owing to haemorrhage from the large
plexus of veins without valves.
XV.--DETECTION OF BLOOD-STAINS, ETC.
Stains may require detection on clothing, on cutting instruments, on
floors and furniture, etc. The following are the distinctive characters
of blood-stains:
(a) =Ocular Inspection.=--Blood-stains on dark-coloured materials, which
in daylight might be easily overlooked, may be readily detected by the
use of artificial light, as that of a candle, brought near the cloth.
Blood-spots when recent are of a bright red colour if arterial, of a
purple hue if venous, the latter becoming brighter on exposure to the
air. After a few hours blood-stains assume a reddish-brown or chocolate
tint, which they maintain for years. This change is due to the
conversion of haemoglobin into methaemoglobin, and finally into haematin.
The change of colour in warm weather usually occurs in less than
twenty-four hours. The colour is determined, not entirely by the age of
the stain, but is influenced by the presence or absence of impurities
in the air, such as the vapours of sulphurous, sulphuric, and
hydrochloric acids.
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