If recent, a jelly-like material may be seen by the
aid of a magnifying-glass lying between the fibres. If old, a
cinnabar-red streak is seen on drawing a needle across the stain.
(b) =Microscopic Demonstration.=--With the aid of the microscope, blood
may be detected by the presence of the characteristic blood-corpuscles.
The human blood-corpuscle is a non-nucleated, biconcave disc, having a
diameter of about 1/3500 of an inch. All mammalian red corpuscles have
the same shape, except those of the camel, which are oval. The
corpuscles of birds, fishes, reptiles, and amphibians, are oval and
nucleated. The corpuscles of most mammals are smaller than those of man,
but the size of a corpuscle is affected by various circumstances, such
as drying or moisture, so that the medical witness is rarely justified
in going farther than stating whether the stain is that of the blood of
a mammal or not. Unfortunately, the corpuscles are usually so dried that
little information regarding their size can be given.
(c) =Action of Water.=--Water has a solvent action on blood, fresh
stains rapidly dissolving when the material on which they occur is
placed in cold distilled water, forming a bright red solution.
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