The most important of these asphyxiant noxious gases are carbonic oxide, carbonic acid, sulphuretted hydrogen, and carburetted hydrogen.

Carbonic Oxide is a much more dangerous poison than is carbonic acid, but poisoning with it in a pure state is rare. It constitutes an ingredient in most vapors produced by burning coke or carbon, especially if the combustion is imperfect. It forms with the coloring matter of the blood a remarkably stable compound of a light red color; in point of fact it is the impossibility of exchanging carbonic acid for oxygen in the lungs which causes death. After death the blood is bright red in hue.

Carbonic Acid Gas.—This heavy inodorous gas is the cause of numerous accidents, owing to the variety of sources from which it is produced. It is formed from burning fuel, from the calcination of limestone or chalk, and it is a product of respiration. It is diffused through wells, coal-mines, and caverns. During fermentation it is largely given off, and accumulates in beer vats. The vapor of charcoal partly owes its poisonous properties to carbonic acid gas, as does that arising from lime and brick-kilns.

In this country suicides rarely resort to carbonic acid gas to accomplish their ends; in France they very frequently do so.

Symptoms.—In its pure state this gas causes death by asphyxia, the glottis becoming spasmodically closed the moment the vapor comes in contact with it. When sufficiently diluted to be inspired it acts by absorption, giving rise to giddiness, headache, vomiting, a tendency to sleep, and loss of muscular power. The heat of the body continues, and the limbs are usually flexible. The countenance gets livid, the respiration becomes hurried and stertorous, and complete insensibility ensues; while the heart’s action, which was at first rapid, soon ceases.

Post-mortem Appearances.—The body is generally swollen and livid, especially about the face. The countenance is not always bloated, sometimes being calm and pale. The limbs are often rigid, the skin is marked with livid patches, and the abdomen is distended with gas. The right cavities of the heart, the lungs, and large veins, are found gorged with venous blood; while the brain and its membranes are usually very vascular, and occasionally there is serious effusion.

Treatment.—Prompt removal to the pure air, cold affusion, and stimulating applications to the chest and extremities, are the best means for resuscitation. If the countenance is bloated, venesection may be performed. Artificial respiration, galvanism, and the inhalation of oxygen gas, have been found useful.

Sulphuretted Hydrogen.—This gas is a very active poison, but from its offensive odor (resembling that of rotten eggs) it is not so liable to be accidentally inhaled as is carbonic acid. It is usually met with combined with other gases, resulting from the putrefaction of animal matter. When breathed in a diluted state, it speedily produces insensibility and death. Workmen long engaged in drains and sewers, or in any atmosphere contaminated with sulphuretted hydrogen gas, suffer from giddiness, nausea, and weakness; these symptoms ending at length in a kind of fever, which is often fatal.

In acute cases there will be little hope of recovery, unless the individual can be quickly removed into the open air, and stimulants, &c., applied. Chlorine gas, well diluted with common air, might be employed, as it breaks up the gas.

Carburetted Hydrogen (Coal Gas).—The symptoms produced by this gas, when mixed with air and inhaled, are those of asphyxia. If the person breathing it should be roused before a fatal quantity has been inhaled, the chief effects may be intense headache, labored and oppressed respiration, quickened action of the heart, sickness, and great loss of power.

In 1841 a family in Strasburg were poisoned by being in an atmosphere contaminated with coal gas, for forty hours. Of the six members, four were found dead, while the father died in twenty-four hours; but the mother recovered. The gas escaped from a pipe which passed under the cellar of the house where this family resided; so that it probably poisoned the air gradually, and gave rise to no suffering to warn the unfortunates.