it
becomes one of the significant regulators of development, with an
indirect hastening or retardation of puberty and maturity according
as it works in excess, or too indolently. It appears thus the blood
brother of the adrenal cortex which also influences the skin pigment
and so susceptibility of the organism to light, brain growth and sex
ripening. It is interesting that Descartes, in 1628, considered the
pineal the seat of the soul.

THE PARATHYROIDS

Sometimes imbedded within the substance of the thyroid in the neck,
sometimes placed directly behind it upon the windpipe, are four tiny
glands, each about the size of a wheat seed, the parathyroids. For
long they were swamped in the nearness of their great neighbor, and
considered merely a variable part of it. There are some who contend
that even today. But it has been proven that they are separate,
individual glands, with a structure and function of their own, and a
definite importance to the body economy.

On the animal family tree they appear early, contemporaneously with
the thyroids. In the embryo they develop from about the same sites.
And very often they look very much alike under the microscope,
especially when the cells are in certain quiescent stage of secretion.
Yet they are wholly independent in nature, activity and business.

First experimenters upon the effects of removal of the thyroid were
confused by contradictory findings with different animals because in
some they would take out the parathyroids at the same time without
knowing it, and in others they would not. That possibility suggested,
more careful dissectors accomplished the job of extirpating the
thyroid while leaving the parathyroids intact and vice versa. In
consequence some definite information about the parathyroids is
available, even though their internal secretion has never been
isolated, or its existence established as more than an inference.

When the parathyroids are removed, an astounding increase in the
excitability of the nerves follow. It is as if the animal were
thoroughly poisoned with strychnine. The slightest stimulus will make
him jump, or throw him into a spasm. When the excitability of the
nerves is measured by an electrical instrument it is found augmented
by from five hundred to one thousand per cent. The reflexes, those
automatic responses of brain and spinal cord to certain stimuli and
situations, become enormously sensitive, so that merely letting the
light into a