. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Respiration and Metabolism 245 diffusion in supplying the tissues with oxygen. This proportionaHty between consumption and tension may apply to pressures above normal atmospheric oxygen tensions in a number of non-regulatory animals, for example, Limax and Limidus. Such a phenomenon indicates either an increase in oxidative processes as a result of the added oxygen partial pressure or a normal unsatura- tion of oxygen in the tissues at atmospheric pressures. Critical oxygen tensions (to), gas pressures above whi
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Respiration and Metabolism 245 diffusion in supplying the tissues with oxygen. This proportionaHty between consumption and tension may apply to pressures above normal atmospheric oxygen tensions in a number of non-regulatory animals, for example, Limax and Limidus. Such a phenomenon indicates either an increase in oxidative processes as a result of the added oxygen partial pressure or a normal unsatura- tion of oxygen in the tissues at atmospheric pressures. Critical oxygen tensions (to), gas pressures above which oxygen consumption is constant despite varia- tions in the partial pressure, are given by Maloeuf^"*- as follows, for four animals, all of which he regards as suffering a state of oxygen unsaturation at normal ambient tensions: Cambarus clarkii Fundulus heteroclitus Limulus polyphemus Triturus pyrrhogaster 186 mm. Hg pOo 190 " " " 220 " " " 760 " " " In contrast to this group of individuals which adjust metabolism according to environmental oxygen tensions stand those organisms with great ability to. 2 4 CONC. 6 e 10 OXYGEN - Fig. 55. Oxygen consumption plotted against oxygen tension for mayfly nymphs, showing dependence in Baetis, independence in Cloeon, and intermediate conditions in Leptophlehia and Ephemera. From Fox et ;" regulate so as to maintain a constant consumption in the face of changing oxygen pressure. Uptake is therefore independent of oxygen tension, at least over a very wide range—, the crustaceans Astaciis and Carciniis, and the molluscs Aplysia and Eledone. In Figure 55 the oxygen consumption of the ephemerid, Cloeon dipterum, is shown constant down to about cc. 02/liter of water, corresponding to 32 mm. Hg partial pressure of ;'' Such a degree of respiratory independence indicates respiratory control or a state of more than adequate oxygen saturation prevailing in
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