The respiration of cardiovascular tissues of the developing chick and adult fowl

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Abstract
The Q02 of cardiac- and aortic-tissue slices from chick embryos, hatched chicks and adult cockerels of various ages was determined by means of a microrespirometer. The embryonic ventricles showed Qo2 values ranging from - 24.3 at 5 days to - 4.1 at 22 days of incubation. After hatching there was a further fall in the O2 uptake of the ventricle, apart from an initial temporary rise. The fall continued into adult life, reaching a QO2 value of -0.5 at the age of 3 years. The atria of hatched chicks and adult cockerels showed higher values for QO2 than the corresponding ventricles. The ventricles in turn gave highir values than the aorta, except in the earlier phases of embryonic life. The continual fall in O2 uptake of atrium, ventricle and aorta, throughout the life of the animal, appeared to be associated with a gradual increase in the amount of connective-tissue fibers present in the tissue.