Metabolism the total activity of a living creature, including respiration, the uptake of energy from food, and the expenditure of that energy in the processes of life. The speed at which this happens is known as metabolic rate; basal metabolic rate is measured when the organism is at rest, and thus shows how efficiently it uses energy.
The study of metabolism has fascinated researchers for centuries. In the 1580s the Italian physician Santorio (or Sanctorius) began a 30-year experiment in which he tried to measure all the inputs and outputs of his own metabolism. He had a chair, bed, and table placed on a platform suspended from a large but accurate balance, and kept scrupulous records of his weight. More significant findings had to wait till the mid-19th century, when chemistry was far enough advanced to tackle the problem properly. The German researcher Jacob Moleschott (see Jane O'Hara-May, 1984) measured the daily intake of protein, carbohydrates, salts, and water by a man of average size and activity, and weighed and analysed body wastes. From these findings he drew up a balance sheet of the metabolism of carbon, oxygen, hydrogen, and nitrogen; this was influential well into the 20th century, when modern biochemists were able to provide more accurate and detailed figures.
