This gas (CO) becomes of interest from the frequency of its poisoning. Most of the cases result from illuminating-gas, which contains 6 to 10 per cent., and is frequently inhaled with suicidal intent. But some come from defective flues of furnaces, coal stoves, charcoal fires, blast furnaces, and the "after-damp" of mines and old wells.

The gas has great affinity for hemoglobin, and prevents the formation of oxyhemoglobin unless oxygen is present in very great excess. But the compound is not a very stable one and usually, if respiration is good and oxygen plentiful, splits up so that all the carbon monoxide will be exhaled by the lungs in from one to three hours. The monoxide does not oxidize to carbon dioxide in the body. Except for its affinity for hemoglobin the gas is physiologically harmless.

The action of the gas is asphyxial, the exclusion of oxygen from the tissues, particularly the central nervous system, being the cause of the symptoms. Haldane found that when mice were placed in oxygen under two atmospheres pressure, so that the plasma would carry enough oxygen to maintain life, carbon monoxide had no toxic effect; but that when the oxygen pressure was removed by exposing the mice to the air, poisoning followed. The toxic symptoms are, therefore, due to an interference with the oxygen-carrying power of the blood. The blood of a man at rest may become nearly one-third saturated without his realizing that anything is wrong (Henderson); and in a few hours he is as fit for vigorous exertion as before. Haldane observed that death occurs when about 80 per cent. of the hemoglobin is disabled, and that the best remedy is the inhalation of pure oxygen.

The symptoms are those of stimulation of the cerebrum and medullary centers, followed by their depression. At first there are headache, dizziness, mental excitement or delirium, slow pulse from stimulation of the vagus center, raised arterial pressure from stimulation of the vasoconstrictor center, dyspnea from stimulation of the respiratory center, and nausea and vomiting from stimulation of the vomiting center. These may be followed by mental dulness or coma, prostration, rapid weak pulse, lowered blood-pressure, slow and shallow or Cheyne-Stokes respiration, fever, loss of control of the sphincters, and convulsions, usually of cerebral (epileptiform) type. The heart continues to beat after respiration has ceased. In the late stages there is sometimes great spasticity or muscular rigidity, so that the patient seems as "stiff as a board." Spiller and others find this associated with bilateral softening of the inner segments of the lenticular nuclei, the softening being due to changes in the minute supplying arteries. Henderson noted a marked acidosis, but obtained no amelioration of the symptoms after large intravenous infusions of 3 per cent. sodium bicarbonate.

A striking characteristic of the poisoning is a subsidence of the acute symptoms, followed by apparent recovery, and then some hours or days later the appearance of serious disturbances of the nervous system, showing in loss of vision, mental derangement, peripheral neuritis, paralyses, epileptiform convulsions, or collapse and death. There may be permanent cardiac weakness.

Acute poisoning is divided by McCombs (1912), who has seen 1000 cases, into three stages, viz.:

1. Before the patient loses consciousness. It is the stage of stimulation.

2. After the patient loses consciousness, respiration still persisting. This is the stage of depression. In this stage or later, cherry-red spots over the cheek-bones, neck, trunk, and thighs may make their appearance, and there may be petechiae.

3. Patient unconscious, no spontaneous respiration. The heart is rapid, weak, intermittent.

Chronic poisoning occurs from the leakage of gas tubes, gas-heated irons, or other continued exposure. It shows in nausea, headache, dizziness, mental depression, lassitude, anemia, loss of appetite and of flesh and strength, and gastric disturbances. It may give any of the symptoms of the first stage of acute poisoning. McCombs, who has studied the men of gas companies, reports polycythemia as quite common, and calls attention to the fact that there are many men who have been much exposed to the gas for many years without any special sign of ill health.

Treatment

1. Of first importance in the mild poisoning is fresh air, and in the severe degrees, oxygen, under pressure, if possible.

2. Artificial respiration when required, deep breathing being essential to the elimination of the gas.

3. Maintenance of body warmth.

4. For the nausea of the mild type effervescing drinks, and for the headache a carminative, such as aromatic spirit of ammonia.

5. Transfusion of blood after a preliminary blood-letting, with manipulation of the heart and artificial respiration, is the method recommended by Crile and Lenhart, who experimented on 16 dogs, giving carbon monoxide until respiration ceased.

Yandell Henderson (1916) says that neither blood-letting nor transfusion can be of use, as the symptoms are not due to retained gas. He found that within one or two hours after the patient had been removed to fresh air the amount of carbon monoxide in the blood was far below the harmful percentage. The damage to the nerve-centers results from lack of oxygen, and has already been done when the patient is rescued.