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CHAPTER XXI 

 DUCTLESS 



.^..Mnapipe GLANDS 



The thyroid gland. An adrenal gland. 



What are ductless glands ? How do they affect the development and the 

 activity of the body? What is the scientific status of gland grafting? 



The glands of the body, that have already been discussed, had 

 ducts to convey their secretions to an outer surface, such as the 

 mouth, stomach, or skin. Certain glands in the body have no 

 ducts, but pass their secretions directly into the blood or lymph. 

 These glands are called endocrine glands (endocrine is from a Greek 

 word which means " to separate within "). These glands manu- 

 facture substances which go into the blood stream, and activate 

 or influence another organ or organs in the body. These manu- 

 factured substances are called hormones (from the Greek word 

 meaning to " excite " or " arouse "). 



Internal secretions. The hormone secretin was mentioned 

 when the digestive system was studied. It is liberated from the 

 wall of the small intestine when the acid food enters from the 

 stomach. It is absorbed directly into the blood and is carried to 

 the pancreas and liver. It stimulates these glands to activity so 

 that the bile and pancreatic juice immediately start to flow. 

 Carefully checked experiments have proven that this activity 

 always takes place. For example, an experiment was given in 

 the chapter on digestion to show that secretin travels through 

 the blood from the intestine to the pancreas. Another interest- 

 ing experiment has been performed to show how digestive juices 



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