. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Respiration and Metabolism 241 underlying metabolic chemical reactions, and, judging from the constancy of the values obtained, represents fundamental relatioftships between different biological systems.^''' '^" By this formula the temperature characteristic—energy of activation or "thermal increment"—of the given system may be found. This value may vary, but in a wide variety of respiratory processes is constant at 11,500 or 16,500 calories. For practical purposes when the log of the reaction rat
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Respiration and Metabolism 241 underlying metabolic chemical reactions, and, judging from the constancy of the values obtained, represents fundamental relatioftships between different biological systems.^''' '^" By this formula the temperature characteristic—energy of activation or "thermal increment"—of the given system may be found. This value may vary, but in a wide variety of respiratory processes is constant at 11,500 or 16,500 calories. For practical purposes when the log of the reaction rate is plotted against reciprocal of absolute temperature the thermal increment is given by the slope of the curve. The inference that such thermodynamic constancy between metabolic processes depends on so-called "master reactions" or that comparable enzyme systems are at work remains to be demonstrated. High basal metabolic rate is condition for homoiothermism and heat regulation. Heat production can be measured by direct calorimetry or may be calculated from CO^ production and O^ consumption. In man with an of , heat is produced to the extent of cal. per liter of O2 con- —. 280 -. 20 40 60 80 100 OXYGEN TENSION - mm. Hg Fig. 53. The interrelation between "maximum steady state" of oxygen consumption, oxygen tension, and temperature in the goldfish, Carassius. The reduction of O2 tension is more effective at higher temperatures. From Fry and Hart.'"" '' The rate of increase in total heat production with body weight varies for different species. The ability of animals to withstand temperature extremes and their metab- olic acclimatization to extreme heat and cold constitute an interesting biological story but one on which there is as yet only scattered information. Some organisms live in environments in which the temperature never exceeds 0° ;^^ Irving^'**•'• cites the case of certain arctic animals, notab
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