144 HUMAN PHYSIOLOGY CHAP. 



urea then enters the blood and is carried along in it 

 until the kidney is reached, where it is picked out and 

 removed from the body. 



Among the other organs that are especially helpful in 

 changing the blood as it passes through them may be 

 mentioned the pancreas, the thyroid bodies, the adre- 

 nals, the lymph nodes and perhaps the spleen. The 

 adrenals are small bodies just above the kidneys, and it 

 is thought that they produce a substance that has an 

 important action upon the heart and arteries. 



The thyroid bodies are situated in the neck, one on 

 either side of the trachea near its upper end. They are 

 dark red in color and somewhat granular in structure. 

 Sometimes these bodies enlarge very much, causing the 

 disease known as goitre. These bodies are important in 

 two ways : first, they remove from the blood certain 

 poisons made by the action of the cells ; second, they 

 produce a substance which is of use in keeping all the 

 organs of the body in a good condition. When the 

 thyroid bodies do not work as they should the blood is 

 deprived of their product, and the person suffers from a 

 disease known as thyroid starvation. 



In children such a condition may result in a form of 

 idiocy (cretonism). A person suffering from thyroid 

 starvation may be helped by eating prepared thyroid 

 glands obtained from the sheep or the calf. The large 

 packing houses have put on the market prepared thyroid 

 glands for this purpose. 



The spleen is located in the abdomen to the left of the 

 stomach. It is an oblong, flat, reddish gray body that 



