HbO2 dissociation curves were determined at different pH values in blood from five adult Hippopotamus amphibius under field conditions. The mean PO2 for 50% saturation at pH 7.4 was 23.9 mm Hg and the Δlog P50/ΔpH was − 0.35. Oxygen carrying capacity varied between 17.8 and 24.6 vol%. The respiratory properties of the blood are considered as normal for a terrestrial animal of this body weight. An anaerobic mixing technique in syringes was used and is discussed in some detail.

The lumbar sympathetic chain was electrically stimulated in different species before and after blocking the adrenergic vasoconstrictor nervous response. Blood flow in the hind limb skeletal muscles was measured. In all species studied, fox, sheep, goat, monkey (five different strains), polecat, rat, badger, opossum rat and hare, stimulation of the lumbar chain before adrenergic blockade resulted in a vasoconstriction. After blocking the vasoconstrictor nervous response stimulation elicited a blood flow increase in fox, sheep and goat. After atropine, the response to stimulation was blocked, indicating that sympathetic cholinergic nerves had been activated. In the other species studied no vasodilator response was observed upon sympathetic chain stimulation. The results suggest that the role attributed to the vasodilator nerves, anticipatory to muscle exercise, are played by other mechanisms in species lacking sympathetic cholinergic vasodilator nerves.