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Updated: May 21, 2025
The Thyroid gland, a somewhat larger body, situated in the front of the neck, just beneath the larynx. We shall deal with this in some detail later on. The Parathyroids, minute organs, four in number, just behind the thyroid. The Thymus, a gland placed just within the thorax, which reaches its maximum size at birth and then gradually recedes until at twenty it has almost disappeared.
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.
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.
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.
Rapid decay of the teeth in childhood should always call attention to the parathyroids. In pregnancy, the teeth suffer particularly because of disturbances of the endocrines. The saying, "A tooth for every child," is said to have its equivalent in every language.
Besides thyroxin, adrenalin, and the libido-producing secretion of the interstitial cells, the substance produced by the paired glandlets, situated behind the thyroid, the parathyroids, have a profound influence upon the vegetative apparatus and the vegetative nervous system. These direct the lime exchanges within the cells of the organisms, including the nerve cells.
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