Basal Metabolism of Rats in Relation to Old Age and Exercise during Old Age

Previous investigations of the basal metabolism of the rat have here been extended by observations upon about 100 over 1 year of age. In most cases periodic measurements of the waking basal metabolism at thermic neutrality (28°C.) and after 24 hours of fasting were begun in the period of middle age and continued throughout the latter half of the normal life cycle. Measurements in the moribund state or immediately premortal physiologic breakdown are not included in the data discussed in this paper, but the normal old-age measurements usually continued until within 2 weeks of the natural death of the animal, and necropsies showed no predominance of any one type of lesion or cause of death. Presumably these rats lived out their natural life cycle.