The Respiratory Function of the Haemo- Globin of the Earthworm

IT was claimed by Davy as early as 1862 that the haemoglobin in the blood of the earthworm has a respiratory function, but subsequent studies have given conflicting results. In the more recent investigations advantage has been taken of the fact that haemoglobin has a greater affinity for carbon monoxide than for oxygen; the oxygen consumption of normal worms is compared with that of worms whose haemoglobin has been put out of action by saturation with carbon monoxide. Using this method, Jordan & Schwarz (1920) concluded that haemoglobin functions as a transporter of oxygen only at low pressures of oxygen (23-30 mm. mercury). Dolk & van der Paauw (1929) criticized this work on the grounds that the pure carbon monoxide to which the worms were subjected for some hours might have affected the respiratory enzymes as well as the haemoglobin, and that because of individual .variation it was not possible to compare directly the oxygen consumption of normal and carbon monoxide-treated worms. They repeated the work with modifications, and again found that haemoglobin was functional as an oxygen transporter only at low pressures of oxygen, below 57 mm. mercury. Their work was done on narcotized animals, and was therefore criticized by Thomas (1935), who, moreover, considered that the conclusions drawn by Dolk & van der Paauw were not justified by the experimental data they published. Thomas reinvestigated the matter, and came to the conclusion that haemoglobin has no respiratory function at oxygen pressures lower than 114 mm., for the oxygen consumption of normal and carbon monoxide-treated worms was the same. Above 114 mm. oxygen pressure the oxygen uptake of normal worms rose sharply, while that of carbon monoxidetreated worms remained constant, but Thomas did not attribute this difference in behaviour to haemoglobin, and one is left with the impression that in the earthworm haemoglobin is functionless as an oxygen transporter at all pressures of oxygen. Thomas's results must, however, be accepted with reserve, for he gives data of experiments on only two normal worms and three carbon monoxide-treated worms.