There is, for every individual, a constant, known as the metabolic rate, or the combustion rate, a reading of the rate at which his cells are consuming material for heat.

Yet, when the time comes for the internal secretion of the thyroid to put in its oar in the metabolic game, its presence or absence makes all the difference in the world to the individual.

The internal secretions constitute and determine much of the inherited powers of the individual and their development They control physical and mental growth and all the metabolic processes of fundamental importance.

These accessory sex-serving traits undoubtedly survived because of their usefulness in external adornment for attracting attention in courtship, in the metabolic requirements of sex combat and the sex act, and in the necessities of caring for the young, until well-grown.

When the reactions go faster, more oxygen and food material are burned up or oxidized, more energy is liberated, the metabolic wheel rotates more quickly, the individual senses, feels, thinks and acts more quickly.