CHAPTER VIII 



THE DUCTLESS GLANDS 



The glands the functions of which have been studied 

 have ducts which carry the results of their labor to the 

 point at which it is to be used in the animal economy. 

 There remain a number of glandular organs, with no 

 ducts, which, nevertheless, exert a great influence on 

 the vital changes of the body, in some instances being of 

 such power that their removal is followed by death 

 within a brief period of time. 



These glands are the thyroid, with its accompanying 

 parathyroids, situated on the trachea near the root of 

 the neck ; the thymus, located in front of the great ves- 

 sels just above the heart ; the adrenal bodies, or supra- 

 renal capsules, perched on the top of each kidney; the 

 pituitary, located at the base of the brain in a peculiar 

 depression of the skull called sella turcica; the pineal 

 gland imbedded in the brain substance near the con- 

 necting link between the third and fourth ventricles ; and 

 the spleen in the abdominal cavity, the largest of all the 

 ductless glands. The secretion of each of these glands 

 is poured directly into the current of the blood and acts 

 through that organ. It is designated an internal secre- 

 tion because there is no obvious apparatus for its dis- 

 charge. Some of the work done by glands with ducts, 

 like the formation of urea by the liver, partakes of the 

 nature of internal secretion. Like the secretin, noticed 

 in the discussion of digestion, these internal secretions 



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