was a Swiss-American animal scientist who made the first accurate measurements of size of organisms versus their rate of energy use (1932). He discovered that the 3/4 power of body weight was the most reliable basis for predicting the basal metabolic rate of animals and for comparing nutrient requirements among animals of different size. Klieber’s Law: MR =aM0.75 where MR is metabolic rate (watts), M is body mass (kg), and a is a constant. Kleiber's law has been confirmed in a broad spectrum of animals spanning more than 20 orders of magnitude in size. He also provided the basis for the conclusion that total efficiency of energy utilization is independent of body size. He also pioneered the use of isotopes to study metabolic processes associated with lactation in cattle (1947).