73$ MEDICAL JURISPKUDENCE Symptoms,—When the gas is inhaled in concentrated form, sudden weak- ness anddizziness is immediately followed by coma and death. Coma may last for three, four or five days even after the patient has been removed from the gas. In one case a patient remained comatose tor eight days and died on the twelfth day after the fatal inhalation.- In such cases there may be "broncho-pneumonia or oedema of the lungs. When inhaled in dilute form, the symptoms are dizziness, headache, noises in the ears, nausea, sometimes vomiting, muscular weakness, drowsi- ness, dilated pupils, retarded breathing, coma and death. In some cases tremors and convulsions may precede death. Nervous and mental symptoms are occasionally manifested after recovery from the effects of the gas. The symptoms may be cerebral haemorrhage, encephalitis, optic neuritis, chorea, spastic paraplegia, retro- grade amnesia, aphasia, mental confusion, transient mania, and dementia. It should be remembered that the symptoms are not noticeable until the haemoglobin is about 20 per cent saturated with carbon monoxide when shortness of breath is observed. When the saturation increases to 30 per cent, there is a slight increase in the rate of the pulse and respiration, followed by headache, nausea and faintness. From experiments made upon himself, Haldane 3 has found that the loss of memory, mental confusion and inco-ordination of movement are the marked symptoms when the haemoglo- bin reaches a saturation of 30 to 40 per cent. Forty to fifty per cent saturation causes collapse and inability to move the limbs, and 60 to 70 per cent saturation causes unconsciousness and rapid death. Haldane has also demonstrated that the haemoglobin is about 80 per cent saturated in deaths from carbon monoxide poisoning. In persons in ill-health death may occur with a much lower percentage of carbon monoxide in the haemoglobin. Spilsbury4 cites a case of suicide in which a young woman suffering from chronic tuberculosis of the lungs died when her blood reached a saturation of only 45 per cent. In two other cases in which the fatal percentage was about 50, one was an old feeble person, and the other was suffering from cancer of the stomach. The presence of 0.01 per cent of carbon monoxide in an atmosphere is considered as a safe limit of concentration, but the presence of 0.02 to 0*05 per cent in an atmosphere causes distinct toxic symptoms. The Board of Trade reported in 1924, that an atmosphere containing 0.25 per cent of carbon monoxide or 3 to 3.3 per cent of coal gas would prove fatal to a healthy adult in about four hours. A smaller percentage would be fatal if the exposure was over a prolonged period. The air containing 1 per cent of carbon monoxide would cause 50 per cent saturation of the blood in fifteen minutes, and 80 per cent in twenty-three minutes, when death would result. However, if the victim exerted himself while absorbing the first part of the carbon monoxide, he might be breathing four or five times as much, and reach the 50 per cent saturation in five minutes.5 Henderson and Haggard ° from their experiments have laid down a standard for calculating the toxic action of carbon monoxide, which depends upon the amount of the gas and -the time of exposure. When the time of exposure in hours multiplied by the concentration of carbon monoxide in parts per 10,000 of air equals 3, there is no perceptible physiological effect. When the product equals 6, there 2. Blytk, Poisons, Ed. V, p. 75. 3. Brit. Med. Jour., July 5, 1930, p. 16. 4. Brit. Med. Jour., July 5, 1930, p. 16. 5. Haldane, Brit. Med. Jour., July 5, 1930 p 16 9, ^f™^^^ Vol. 16, p. 229; Brit Med, Jour, Jan.