6o HUMAN PHYSIOLOGY CHAP. 



small blood vessels that easily become gorged with 

 blood (congested) when any part of the body is exposed 

 to cold. The phlegm that gathers in these organs when 

 one has an ordinary cold seems to be a natural salve to 

 protect the inflamed membrane against irritating foreign 

 substances. 



Catarrh is an inflammation of the nasal passages that 

 continues for a long time and may become the cause of 

 ulcers. A "cold in the head" is due to an inflamma- 

 tion of the mucous membrane of the pharynx and the 

 tubes that extend to the ears and eyes. When the con- 

 gestion is confined to the larynx, as when a cold makes 

 it difficult or impossible to talk, we call it laryngitis. 

 A similar inflammation of the trachea and bronchial 

 tubes is known as bronchitis. The little muscle fibers 

 of the bronchioles that lead to the air sacs may be- 

 come irritated and contract so as 

 to prevent the air from entering the 

 sacs as freely as it should ; such a 

 condition of difficult breathing is 

 sometimes called asthma. 



The inflammation may not re- 

 main in the air passages only but 

 FIG. 28. -Bacteria of extend down into the air sacs them- 



pneumonia (Pratt). 



selves. They may become so filled 

 that breathing becomes painful and difficult. This con- 

 dition may bring on the disease known as pneumonia. 



All of the diseases mentioned are not mere, conges- 

 tions and inflammations. They are due to attacks of 

 certain germs. The congestion affords an excellent 



