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. 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. The
haematin of old stains dissolves very slowly, so employ a weak solution
of ammonia, and this will give a solution of alkaline haematin. Rust is
not soluble in water.

(d) =Action of Heat.=--Blood-stains on knives may be removed by heating
the metal, when the blood will peel off, at once distinguishing it from
rust. Should the blood-stain on the metal be long exposed to the air,
rust may be mixed with the blood, when the test will fail. The solution
obtained in water is coagulated by heat, the colour entirely destroyed,
and a flocculent muddy-brown precipitate formed.

(e) =Action of Caustic Potash.=--The solution of blood obtained in water
is boiled, when a coagulum is formed soluble in hot caustic potash, the
solution formed being greenish by transmitted and red by reflected
light.

(f) =Action of Nitric Acid.=--Nitric acid added to a watery solution
produces a whitish-grey precipitate.

(g) =Action of Guaiacum.=--Tincture of guaiacum produces in the watery
solution a reddish-white precipitate of the re