. The comparative physiology of respiratory mechanisms. Respiration. 70 RESPIRATORY MECHANISMS metabolism in not less than 40 minutes. Oxygen debts of 5-6 liters are easily reached. In several cases it was found that breathing of 50% oxygen which increases the supply to the working muscles would increase the amount of oxygen debt which could be built up (Hill, Long and Lupton, 1924). At a low oxygen pressure (high altitude) the maximum oxygen debt is definitely reduced (H. T. Edwards, 1936). A comparatively small part of the oxygen debt is caused by depletion of oxygen stores in the blood and
. The comparative physiology of respiratory mechanisms. Respiration. 70 RESPIRATORY MECHANISMS metabolism in not less than 40 minutes. Oxygen debts of 5-6 liters are easily reached. In several cases it was found that breathing of 50% oxygen which increases the supply to the working muscles would increase the amount of oxygen debt which could be built up (Hill, Long and Lupton, 1924). At a low oxygen pressure (high altitude) the maximum oxygen debt is definitely reduced (H. T. Edwards, 1936). A comparatively small part of the oxygen debt is caused by depletion of oxygen stores in the blood and in the muscle haemoglobin. All the rest was ascribed by Hill and his co- workers to lactic acid produced in the working muscles, but there is now a general agreement that a large fraction of the debt (perhaps about 1/2) is "alactacid": due to other and so far unknown split products. During rest man cannot contract an oxygen debt, except in experiments in which the blood supply to some part of the body (, the legs) is cut off. In experiments of this type a complete cessation of blood-flow to a limb can be tolerated for more than 20 minutes, and the muscles concerned will absorb afterwards an extra amount of oxygen amounting to at least 1 liter. As we shall see presently, certain animals are able to build up an oxygen debt even during rest and utilize this power in prolonged diving. The lungs and respiration of birds. The respiratory mech- anisms of birds are definitely adapted to the function of Fig 42. Metal cast of lungs and air ffi , a§ evidenced b the sacs ol pigeon. Note recurrent bronchi ° ' J from lower air-sacs. (Scharnke.) fact that birds which do not. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Krogh, August, 1874-1949. Philadelphia, University of Pennsylvania press
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