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 of a constant figure.  Under such conditions, the level of energy production is bound to be low, and to remain low, and the modus of its mobilization slow and unwieldy.  With thyroid is introduced the trick of catalysis, or the speeding up of the vital chemical reactions, through the agency of an intermediate which accelerates the process.  It is par excellence the great catalyst of energy in the body. (A catalyst is an intermediary like the trace of water, which will bring about an explosion between dry oxygen and hydrogen that without it have stayed inert with the strongest currents of electricity.) Thus it supplies a mechanism not only for quantity output of that subtle reality we label energy, but also an apparatus for varying the available amount of it, and for permitting the maximum range in ease and rapidity of its utilization.  The thyroid is still another device of life for procuring more and more variation and differentiation, its goal, as far as we can peer through the opalescent screen upon which its manifestations quiver.

From another point of view, the thyroid may be looked upon as the organ evolved for maintaining the same amount of iodine in the blood as there is in sea water.  Sea water was our original habitat, since, like Venus, we have all come up out of the sea.