cent. in the atmosphere is immediately
fatal.

_Symptoms._--When in _large amount_, insensibility comes on at once;
when in _very small amounts_, headache, giddiness, noises in the ears,
nausea, and vomiting, with prostration, insensibility, and coma. There
may be convulsions. Even in cases which recover, permanent impairment of
the brain may result.

_Post-Mortem Appearances._--The blood is bright red in colour, due to
the interaction of carbonic oxide with haemoglobin. A rosy hue of the
skin-surface and viscera is often noticed. Bright red patches of colour
are found over the surface of the body. The spectrum of the blood is
characteristic.

_Treatment._--Ammonia to the nostrils, inhalation of oxygen, cold douche
in moderation, artificial respiration, transfusion of blood.

=Coal Gas.=--Coal gas contains light carburetted hydrogen or marsh gas,
olefiant gas, ammonia, sulphuretted hydrogen, carbonic acid, carbonic
oxide, free hydrogen, and nitrogen. Coal gas has an offensive odour,
burns with a yellowish-white flame, yielding water and carbonic acid.
Cases of poisoning often due to escape of gas into the room.

_Symptoms._--Headache and giddiness, foaming at mouth, vomiting,
convulsions, tetanic spasms, stertorous breathing, dilated pupil. The
breath smells of gas; there is profound stupor; the patient, if alive,
exhales gas from the lungs when removed into a fresh room or into the
air. Smell of gas in the room and in patient's breath.

_Post-Mortem Appearances._--Pallor of skin and internal tissues; florid
colour of neck, back, and muscles, if much CO present in the coal gas;
fluid florid blood; infiltration of lungs.

_Treatment._--Fresh air, artificial respiration, cold affusion,
diffusible stimulants; inhalation of oxygen freely.

=Sulphuretted Hydrogen= is characterized by its odour, like that of
rotten eggs. It is extremely poisonous.

_Symptoms._--Giddiness, pain and oppression in stomach, nausea, loss of
power; delirium, tetanus, and convulsions.

_Post-Mortem Appearances._--Fluid and black blood (sulph-haemoglobin),
smell of H_{2}S on opening the body; loss of contractility of muscles,
rapid putrefaction.

_Treatment._--Fresh air, stimulants, inhalation of chlorine.

_Tests._--Acetate of lead throws down a brown or black precipitate
according to the quantity of the gas.

=Sewer Gas.=--Cesspool emanations usually consist of a mixture of
sulphuretted hydrogen, sulphide of ammonium, and nitrogen;