It is important to get clearly in mind these subtle inter-reactions of the different ductless glands.  They may be antagonistic in their end effects because of the opposed functions of the nerves or organs stimulated.  There are inhibitions and restraints produced when a gland will send out its secretions to stop another gland secreting.  There are compensations resulting when because of insufficiency of a gland, others will endeavour, by manufacturing more of their own secretion, to compensate for the loss.  There are mutual co-operations, partnerships, when a gland will oversecrete to assist another, or in response to another which is also oversecreting.  There are losses of balance, so that when one gland ceases secreting, another will simultaneously or soon after.  Normal secretion, oversecretion or undersecretion are thus adjusted, but leave a train of after effects.

So with loss or insufficiency of the thyroid, there may be pituitary overgrowth, because the pituitary may act as vicar for the thyroid.  The thyroid and thymus are antagonistic, for the thyroid hastens differentiation, puberty and the coming of sexual maturity, while the thymus delays and retards them and prolongs the period of childhood.  The thyroid and the pancreas are antagonists, for when the thyroid has been excised, the pancreas appear no longer necessary to act as a break upon the mechanism of sugar liberation into the blood from the liver.  The thyroid stimulates the interstitial glands, for menstruation and pregnancy are impossible with no thyroid or an insufficient thyroid.  Removal of the pituitary makes the thymus shrink because the restraining influence of the latter is no longer needed.  But there is an enlargement of the thyroid to compensate.  In castrates there is an increase in the size and number of the cells of the anterior pituitary, again a compensation or substitution effect.  The pituitary and the adrenal cortex are mutually assistant, alike in their influence upon the tone of the brain and sex cells.

THE KINETIC SYSTEM

So there are combinations of glands to assist or restrain others, or to control a body function, or to determine the domination or abeyance of an instinct.  One such has been named the kinetic system because it comes into play in situations which demand prompt adaptation without hesitancy, and a consequent immediate transformation of static or stored energy into kinetic or active energy.  According to this conception the brain, the adrenals, the liver, the thyroid and the muscles together constitute a machine very much like an automobile.  The self-starter of the machine is the brain, with storage battery (composed of stored past memories) and ignition combined.  The thing seen without, or the idea felt within, act as the initial sparks, while the adrenals, as the carburetors, permit the freer flow of fuel, sugar, from the liver.  The thyroid works as the accelerator, the original impulse