s cells are consuming material for heat. The metabolic
rate is thus a gauge of the energy pressure within the organism.
It may be calculated by measuring the amount of carbon dioxide gas
exhaled during a unit of time, and the number of calories of heat
radiated by the skin simultaneously. A simplified device has lately
rendered it practicable to make actual determinations by a few
five-minute readings of the rate of oxygen absorption by the lungs.
Plummer, also connected with the Mayo Foundation, has shown that what
would amount to less than a grain of the thyroxin would more than
double the amount of energy produced in a unit of time. To be exact,
one milligram of thyroxin increases the metabolic rate two per cent.
That illustrates some of the power of the internal secretion of the
thyroid and its importance to normal life.

THE MOBILIZATION OF ENERGY

But not only is the height of pressure of energy in the cells
controlled by the thyroid. The mobility of that energy is also
controlled. Without it, rapid and large fluctuations of energy output,
and elasticity and flexibility of energy mobilization for any sudden
mental or muscular act, let alone an emergency, become impossible. A
woman suffering with myxedema, the condition described by the English
physician Gull as a cretinoid state supervening in the adult life
of woman, has an insufficient amount of thyroxin in her blood and
tissues. She is clumsy and awkward and will stumble when endeavoring
to walk upstairs. Any effort is almost paralyzed because the range
of fluctuation of energy, the ability to mobilize energy, in turn
dependent upon an ability to increase the metabolic rate, is limited.
In slang phrase, she cannot step on it. Her existence is set to go at
a rate in the neighborhood of forty per cent below the normal. By the
administration of thyroxin, her metabolic rate can be raised to any
desired figure, the spark can be adjusted, so to speak, to any point
we like, and it can be so maintained for years.

In the normal animal, to be sure, the internal secretion of the
thyroid is not absolutely essential to life. So it contrasts with the
hormone of the minute parathyroids placed so closely to it, a minimum
dose of which is absolutely a prerequisite for continued life. The
fundamental chemical reactions within the cells occur in the complete
absense of thyroxin. But they go on in a relatively fixed, rigid and
unvarying way, confined within the narrow limits o