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Updated: June 12, 2025
Fear and anger, respectively bound up with the activities of the adrenal medulla and cortex, we shall see, provide as good exemplars as any of this process. The response of the ductless glands to situations varies with their congenital capacity, and acquired susceptibility. Capacity is a question of internal chemistry, modifiable by injury, disease, accident, shock, exhaustion.
Experimental work has also demonstrated the functions of the suprarenal glands and explained the symptoms of Addison's disease, and chemists have even succeeded in making synthetically the active principle adrenalin. There is perhaps no more fascinating story in the history of science than that of the discovery of these so-called ductless glands.
Moreover, as Cecca and Zappi found, removal of the ovaries has exactly the same effect on the abnormal development of the other ductless glands as has removal of the testes. It is of interest to point out that the internal secretion of the ovaries and its important functions seem to have been suggested before any other secretion than the sperm was attributed to the testes.
It was not until 1869 that Brown-Séquard first suggested that an important secretion was elaborated by the ductless glands and received into the circulation, but that suggestion proved to be epoch-making.
"These hormones," added Kennedy, "are closely related to many reactions in the body, such as even the mother's secretion of milk at the proper time and then only. That and many other functions are due to the presence and character of these chemical secretions from the thyroid and other ductless glands. It is a fascinating study.
If Harvey had not discovered the circulation of the blood, some one else would have. The wonder is that it was not discovered ages before. So far as I know, no one has yet discovered the function of the spleen, but doubtless in time some one will. It is only comparatively recently that the functions of other ductless glands have been discovered.
Nowadays, we see its domain as a limited monarchy, if not indeed as one sovereign state of a republic, a member equal but not superior to the others of a board of directors. Its true business comes down to two particular rôles: first, the production of ova, and, second, the secretion of a hormone or hormones. Over the other functions once supposed its monopoly, all the ductless glands rule.
It is obvious that whatever the excitant the physico-chemical action of the brain and the ductless glands cannot be reversed the effect of the stimulus cannot be recalled, therefore either a purposeful muscular act or a neutralizing act must be performed or else the liberated energy must smoulder in the various parts of the body.
But as each tooth is a miniature organ, inspectable by the eye as a unit, the action of the ductless glands is more obviously reflected for the observer to read. By their teeth shall ye know them.
For instance, under the same stimulation, one may run and another may fight, depending perhaps on the secretions that the ductless glands empty into the blood. No machine can act except according to its make-up. Even an ignorant person, who finds that the same stimulant produces different results on different machines, would know that the structures are not the same.
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