The Respiratory Function of the Haemoglobin of the Earthworm1

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Abstract
The oxygen consumption of earthworms (Lumbricus herculeus Savigny) has been measured at 10°C., in the dark, in atmospheres containing 20, 10, 5, 2.5 and 1% of oxygen (i.e. at partial pressures of oxygen of about 152, 76, 38, 19 and 8 mm. mercury), with and without the addition of enough carbon monoxide to saturate the haemoglobin of the blood. In the absence of carbon monoxide the rate of oxygen consumption was significantly the same at 152 and 76 mm.; below 76 mm. it fell sharply. The rate of oxygen consumption of carbon monoxide-treated worms was significantly lower than that of normal worms at oxygen pressures of 152, 76, 38 and 19 mm. but not at 8 mm. The respiration of slices of earthworm has been measured in atmospheres containing 20% of oxygen, and 20% of oxygen together with 20% of carbon monoxide. The rate of respiration in the presence of carbon monoxide was 110% of that in its absence. It is concluded that the lowering of the rate of respiration of whole worms caused by carbon monoxide was not due to inhibition of respiratory enzymes, but to its effect on haemoglobin. Haemoglobin therefore transports oxygen at atmospheric as well as at lower partial pressures of oxygen. Less oxygen was carried by haemoglobin at 19 mm. than at 38 mm. It is deduced that the loading pressure of earthworm haemoglobin is higher than 19 mm. The haemoglobin, of the blood was responsible for supplying about 23% of the respired oxygen when the oxygen pressure was at 152 mm., 35% at 76 mm., 40% at 38 mm.; and 22% at 19 mm. of oxygen.