DISEASES CAUSED BY BACTERIA 299 



How We Catch a Cold. Because of the germicidal properties 

 of the mucus, the bacteria which are constantly living in the body 

 are unable to do any injury or produce disease until the body con- 

 dition is altered or weakened so that the bacteria may live. There 

 are two ways of catching cold ; first, when the bacteria in the mucus 

 of the nasal passages or pharynx become sufficiently active to 

 cause inflammation; second, when additional bacteria come from 

 the outside. The bacteria immediately begin to multiply and soon 

 attack the mucous membrane. The first result is a large secretion 

 of mucus which represents nature's method of destroying or wash- 

 ing out the bacteria. This mucous secretion is deficient in bacteri- 

 cidal properties and only furnishes a better breeding ground for the 

 bacteria; first we see a thin watery discharge from the nose which, 

 as the bacteria multiply, becomes gradually more and more tena- 

 cious and finally assumes a yellowish color. The toxin which is 

 produced by the germs enters the blood, producing backache, 

 pains in the joints, and general feeling of illness. The body at 

 once starts to manufacture germicidal substances to kill the bac- 

 teria and neutralize the toxins; hence the person recovers from a 

 cold. 



It will be seen that colds are contagious, and may be obtained 

 from people in assemblies, school rooms, street and railway cars, 

 through the use of the common drinking cup and even from the 

 drinking fountain. 



The mucus-secreting apparatus has several definite purposes: 

 (1) As a covering film to protect the membranes from the effects 

 of extremely cold air; (2) to aid in warming the air sufficiently 

 before it is passed on to the lungs; (3) to gather from the air bac- 

 teria and other impurities; (4) as a germicidal power to destroy 

 bacteria which enter the mucus. 



Diphtheria. Diphtheria germs are usually found in the larynx 

 and mouth. These germs live in material which has come from the 

 throat of a diphtheria patient. A slight attack of diphtheria 

 often causes sore throat only, but if the germs grow rapidly the 

 attack is so severe that death follows in a few days. The germ 

 may cause death by closing the throat, but, as a rule, death 

 is caused by the powerful toxin which the germ produces. The 



