There is, however, another by-product of the work on an energy machine, and that is heat.
The combustion of foodthat is, its chemical union with oxygengoes on continuously in the body, and by a delicate regulatory mechanism keeps the body at the even temperature of about 98% F.
All of the processesboth the building up of heat and its dissipation by the body, and the chemical interchanges of various kindswhich go to make up the machinery of the body, are called “metabolism.” The sum of all of them is called “basal metabolism,” and this can be easily measured.
The first experiments in trying to measure basal metabolism took the amount of heat an animal gave off as a standard. The animala cat or guinea pigwas placed in a vessel surrounded by ice. After a certain length of time the amount of ice that had melted was measured; as the number of calories required to heat a given amount of ice is well known, it was easy to calculate the amount of heat given off by the animal.
More modern instruments have improved on this old ice calorimeter and use the amount of oxygen consumed as the measuring rod of basal metabolism.
The measurement of basal metabolism is very useful in diagnosis in certain cases: it is known that certain forms of goiter raise the basal metabolic rate very greatly.