um of this animal's blood will then give a white
precipitate only when brought into contact with dilute solutions of
human blood, but with the blood of no other animal. This is known also
as the 'biologic,' or Uhlenhuth's test.

=Rust Stains.=--These are yellowish-red in colour, and do not stiffen
the cloth. The iron may be dissolved by placing the stain in a dilute
solution of hydrochloric acid, when, on adding ferrocyanide of
potassium, Prussian blue is produced.

=Fruit Stains= are seldom so dark as blood-stains. Solutions of these do
not change colour or coagulate on boiling; ammonia changes the colour to
blue or green; acid brightens the original colour, while chlorine
bleaches it.

=Hairs.=--Human hairs must be identified and distinguished from those of
the lower mammals. If the hair has been pulled out from the root, the
microscope will show that the bulbous root has a concave surface which
fitted over the hair papilla, or that the root is encased in a fatty
sheath.

=Fibres of Clothing.=--Microscopically, wool fibres are coarse, curly,
and striated transversely; cotton fibres appear as flattened bands
twisted into spirals; linen fibres are round, jointed at frequent
intervals, with small root-like filaments; silk fibres are solid,
continuous, and highly glistening.

XVI.--DEATH BY SUFFOCATION

_Signs and Symptoms._--There are usually three stages:

1. Exaggerated respiratory activity; air hunger; anxiety; congested
appearance of face; ringing in ears.

2. Loss of consciousness; convulsions; relaxation of sphincters.

3. Respirations feeble and gasping, and soon cease; convulsions of
stretching character; heart continues to beat for three to four minutes
after breathing ceases.

_Post-Mortem Appearances--External._--Cadaveric lividity well marked;
nose, lips, ears, finger-tips almost black in colour; appearance may be
placid or, if asphyxia has been sudden, the tongue may be protruded and
eyeballs prominent, with much bloody mucus escaping from mouth and nose.

_Internal._--The blood is dark and remains fluid; great engorgement of
venous system, right side of heart, great veins of thorax and abdomen,
liver, spleen, etc. Lungs dark purple in colour; much bloody froth
escapes on squeezing them; mucous lining of trachea and bronchi
congested and bright red in colour; air-cells distended or ruptured;
many small haemorrhages on surface of lungs and other organs, as well as
in their substance (_Ta