azingly minute
compared with the quantity of whole gland necessary. Moreover, a dose
of thyroxin appears to last an organism in need of it over a period of
time; the other has to be administered continuously.

Studies with thyroxin carried on in recent years have rounded out the
whole concept of the business of the thyroid in the body economy.
One may sum it up by saying that the thyroid secretion is the _great
controller of the speed of living_. The more thyroid one has, the
faster one lives; the less one has, the more slowly one lives.

That is not to imply any direct proportion between the amount of
thyroid secretion in an individual, and the length of life to which he
is destined. The speed of living, in the chemical sense (which is the
fundamental sense), and the rate at which the chemical reactions go on
that constitute the process of life, are dependent upon the thyroid.
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.

Likening one energy machine to another, the thyroid may be compared
to the accelerator of an automobile. That is a rough and superficial
comparison because an accelerator lets in more of the fuel to be
burned up, while the thyroid makes the fuel more combustible. It thus
resembles more the primer, for a rich mixture of gasoline and air
burns at a greater velocity than a poor one. But the action of thyroid
could really be simulated only by some substance that could be
introduced into the best possible of gasoline mixtures, to increase
its combustibility by a hundred per cent or more. For that is what
thyroid will do to our food. Nor has it only this destructive or
combustion side. Withal there is at the same time a constructive
action, for the process frees energy to be used for heat, motion or
other need. The thyroid, therefore, in addition to its role as an
accelerator, acts, too, as the efficient lubricator for energy
transformations. So we see it as accelerator, lubricator and
transformer of our energies.

THE GLAND OF ENERGY PRODUCTION

The isolation of thyroxin has made possible the determination of the
influence of the thyroid hormone upon the evolution of energy in any
higher animal organism. There is, for every individual, a constant,
known as the metabolic rate, or the combustion rate, a reading of the
rate at which hi