88 POPULAR SCIENCE MONTHLY. 



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 ulti- 

 mately 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 myxoedema, 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 impor- 

 tant constituent. It appears to be the office of the thyroid to manu- 

 facture 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 con- 

 tain 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' influ- 

 ence 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. 



Jhe 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 

 Schafer 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 

 chano-es occurring in the body, is that of the ovaries. It has long been 

 familiar to stock farmers that the removal of these organs greatly 



