=Carbon Dioxide.=--Carbon dioxide is a product of combustion and respiration, and is generated in many ways during fermentation. It is a constituent of _choke damp_ due to explosions in coal-mines, and is given off from lime-kilns, brick-kilns, and cement-works. It is often met with in dangerous quantities in wells and in brewers' vats. From 10 to 15 per cent. in the atmosphere would prove fatal, but even 2 per cent. inhaled for long would produce serious symptoms. The proportion usually present in air is 0.04 per cent. _Symptoms._--Inhalation of the _pure_ gas causes spasm of the glottis, insensibility, and death from asphyxia, at once; _diluted_, causes sense of weight in forehead and back of head, giddiness, vomiting, somnolence, loss of muscular power. Insensibility, stertorous breathing, lividity of face and body, and death from asphyxia. Convulsions occasionally. _Post-Mortem Appearances._--Face swollen and livid, or calm and pale; lividity is most marked in eyelids, lips, ears, etc.; limbs usually flaccid, abdomen distended; right side of heart, lungs, and large veins, gorged with dark-coloured blood. Brain and membranes congested. _Treatment._--Pure air, cold affusion, stimulants, artificial respiration, galvanism, inhalation of oxygen, venesection, transfusion. =Carbonic Oxide.=--This is one of the most poisonous of gases. It is evolved in the process of burning charcoal and coke in stoves or furnaces. Water-gas, obtained by passing steam over heated coke, contains 40 per cent. of the substance, the remainder being chiefly hydrogen. It forms the chief part of the deadly 'choke damp' after an explosion in a mine. Two per 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.