Page:Popular Science Monthly Volume 59.djvu/98

88 formed by a gland and taken up from it by the blood or lymph. An ordinary external secretion is discharged by a special duct into the proper receptacle, bile, for example, into the gall-bladder, and ultimately into the intestine; urine into the urinary bladder, and so on. Some of the glands which produce important internal secretions have no ducts. Such are the thyroid glands, two insignificant looking reddish bodies situated in the neck, one at each side of the windpipe, a little below the larynx. It had been long known that disease of these glands, commencing in childhood and leading to the enlargement which we call goitre, was often associated with a condition of idiocy (cretinism). Interest in their functions was greatly stimulated by the discovery that excision of the thyroids was followed by grave changes resembling those found in a disease called myxedema, and that the symptoms produced by excision, as well as those present in the natural disease, could be removed, and health restored, by feeding the patient with the raw or slightly cooked thyroids of animals or with certain extracts prepared from them. Much work has been devoted to the isolation in a pure form of the active substances, one of which contains iodine as an important constituent. It appears to be the office of the thyroid to manufacture for the use of the body a constant supply of these substances, which are necessary for the due maintenance of certain of its functions. In the absence of the natural supply, similar materials produced by the corresponding glands in animals can be utilized.

The suprarenal or adrenal bodies, situated just above the kidneys, are another pair of ductless glands whose function is of extraordinary importance in proportion to their size. It has been shown that they contain a substance which when injected into the blood in animals, or painted, say, on an inflamed eye in man, causes a marked narrowing of the small arteries; and it has been surmised that this substance, oozing slowly from the glands into the blood, exerts a bracing or 'tonic' influence on the muscular fibers of the heart and blood vessels, and helps to keep them in proper condition for their work. Certain it is that death follows their removal in animals, while their disorganization in man is associated with the peculiar and fatal condition termed Addison's disease.

The pituitary gland, a small body attached to the base of the brain, is in the same category. It seems to be of great importance, if not absolutely indispensable to life. Extracts of the gland, as Howell and Schäfer have shown, produce decided effects upon the pressure of the blood when injected into the vessels.

One of the most interesting examples of an internal secretion which is not necessary to life but which yet profoundly affects the chemical changes occurring in the body, is that of the ovaries. It has long been familiar to stock farmers that the removal of these organs greatly