Ductless Glands
those whose secretions are directly absorbed by the blood or lymph, not discharged through ducts, as in ordinary glands. The principal ductless glands of the body are the thyroid, the suprarenals, and the pituitwaves reaching an observer from a mov-ary gland. Certain other glands or ing body on account of the latter's approach or recession. When a body which is emitting such waves is at the same time approaching the observer, the number of vibrations reaching the latter in a unit of time is of course increased; or, in other words, the wave-lengths are diminished, thus altering the color of any light emitted or raising the pitch of any sound.
A familiar example of the Doppler effect is the rise of pitch in a locomotive whistle, followed by its fall, as it passes a car window. Doppler's Principle has long been used in astronomy, in connection with the spectroscope, to determine the radial velocity of stars: - that is, the speed with which stars are moving toward or away from the solar system.
It has also been used to prove and measure the rotation of the sun and various planets, as well as to measure the orbit of the earth. In the field of sound, the Doppler effect has recently been utilized in a signaling device invented by Mr.
Anders Bull, which indicates to receivers the direction of the signal by means of organs have external ducts and yet also elaborate internal secretions, like the true ductless glands. Such are the pancreas, the liver, and the reproduction glands. Until recently the functions of the true ductless glands were but little understood. They are now known to be the principal regulators of a number of important bodily functions, and their failure to secrete in proper measure is sometimes attended by disastrous results.
The failure of the thyroid gland, for example, produces the disease called myxedema and is also responsible for cretinism, both of which may be cured or greatly ameliorated by the proper administration of thyroid preparations to the patient. Within very recent times a new field of therapy has been opened by the use of the secretions of the ductless glands in medicine. According to Dr. Steinach of Vienna, old age is due to certain changes in the chemical secretions of the ductless glands. He has found that they may be temporarily reinvigorated. (See OLD AGE.) E