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Journal of Experimental Biology 27,158-174 (1950)
Published by Company of Biologists 1950

The Physiology of Carbon Dioxide Transport in Insect Blood : Part I. The Form of Carbon Dioxide Present in Gastrophilus Larva Blood

L. LEVENBOOK ¹

¹ Molteno Institute, University of Cambridge

1. The pH of the blood of the third instar Gastrophilus larva is 6.64 at 38° C. with a pH-temperature coefficient of -0.007 Per 1° C. rise in temperature.

2. The total CO₂ content of the blood varies from 40.6 to 131.4 vol. % with an average of 72.4 vol. %. The CO₂ content of the tissues minus the cuticle is very close to, and follows the variations in, the CO₂ content of the blood.

3. The CO₂ tension in the blood is from 300 to 500 mm. Hg. From 30 to 50% of the CO₂ is in solution, the rest in the form of bicarbonate. Carbamate formation does not occur in the blood.

4. The ‘apparent’ dissociation constant for carbonic acid, (pK'₁), has a value of 6.08 (S.D. ±0.06) at 38° C. and 6.19 (s.d. ±0.13) at 16° C.

5. CO₂ dissociation curves have been drawn for 38 and 16° C. The slope of the curves indicates that the whole of the CO₂ is given off at zero CO₂ tension, and that the blood is adapted for functioning at high CO₂ tensions.