The question of the basal metabolism at various ages has been discussed in Paper 12 of this series, and the references to the literature have already been published. It was apparent that our knowledge of the energy exchanges in old age depended almost entirely on the careful work of Magnus-Levy and Falk1who studied five old men and seven old women. These results were used by us in drawing the curves which indicated the average level of metabolism at various ages, but it was apparent that after the age of 43 the points on the chart were scanty. This present work is an attempt to fill in the gap. An effort was made to find men 90 to 100 years old, but it was impossible to obtain suitable subjects. The age limits were then reduced to between 75 and 85 years, and, after much labor