180 



RESPIRATION 



necessitate mouth breathing. This not only allows dust and other 

 foreign particles to pass into the lungs, but tends to alter the shape 

 of the jaws and facial features. Malformations of teeth are fre- 

 quently caused by adenoids. 

 Mouth breathing is usually 

 a forced breathing and 

 frequently alters the shape 

 of the chest. 



In the lower part of the 



Thickened mucous membranes may form abnormal throat, On either Side, are 

 growths, known as adenoids, in the back of the nasal ,, , , . , 



passageways. Tonsils are the normal growth of lym- Small maSSCS OI lympnoid 



tissue called tonsils. The 



function of the tonsils is not understood exactly. They are 

 thought, when in a normal condition, to help protect the body 

 from infection by acting as filters and preventing the entrance 

 of bacteria. If they become infected with bacterial growths, they 

 serve only as centers of infection. When they are infected, the 

 pus in them passes directly into the lymph and then into the blood. 

 This may cause such conditions as rheumatism, anaemia, or pro* 

 duce an undesirable heart condition. If the tonsils become much 

 enlarged, they fill the throat cavity and interfere with the passage 

 of air to the lungs and of food to the gullet. Inflammation of the 

 tonsils is called tonsillitis. 



Problem. Study of the lungs. 



Secure the lungs and windpipe of a sheep or lamb from the butcher. 



I. Try to cut the windpipe or trachea. 



A. Describe the structure. 



B. What is the value of the presence of cartilage in the trachea? 



C. Describe the arrangement of the cartilage in the trachea. 



II. Observe the appearance of the lungs. 



A. Describe the outer shiny covering. Discuss the functions of the 

 covering. 



B. Describe the structure of the lungs, including the shape, texture, 

 color, and tissues present. 



