474 CERTAIN OTHER BACTERIA 



these bacteria gain a foothold and produce the condition known as 

 a cold. Blood congests in the mucous membrane which becomes 

 swollen and causes a profuse flow of mucus. The mucous mem- 

 brane of the tear ducts may also swell and the tears will flow con- 

 tinuously. If the inflammation spreads to the Eustachian tubes, 

 they may become closed and hearing is temporarily impaired. If 

 the infection extends to the middle ear, earache usually results. 

 Sometimes infection may extend to the cavities in the bones of 

 the front of the skull called the sinuses and cause inflammation 

 or sinusitis. If the infected material is retained in the sinus, the 

 condition usually becomes chronic. 



A chronic cold is known as catarrh. If the disease extends 

 down into the bronchial tubes, the condition is known as bron- 

 chitis ; the inflammation of the finer bronchi may cause broncho- 

 pneumonia. People w^ho work indoors and at sedentary occupa- 

 tions are more likely to suffer from colds than persons who liye an 

 outdoor life, as dust, dry air, and noxious gases are continually 

 irritating the respiratory tract and making it susceptible to infec- 

 tion. These same predisposing factors increase the likelihood of 

 the disease extending into broncho-pneumonia. This type of pneu- 

 monia is unlike lobar pneumonia. The latter is caused by a specific 

 microorganism, the pneumococcus. Broncho-pneumonia may be 

 caused by any bacteria that infect the bronchial tubes and air 

 sacs. 



Colds are frequently neglected and considered of trivial im- 

 portance. Each cold lowers the resistance and vitality of the 

 body to such an extent that the sufferer is likely to contract other 

 infections. This may hasten the progress of a serious disease like 

 tuberculosis. Every effort should be made to prevent colds. Once 

 a cold is contracted, the best possible care should be taken to 

 avoid any secondary infections. 



Method of spread. Even with many of the predisposing fac- 

 tors present, a cold does not develop unless there is an exposure 



