42O APPLIED PHYSIOLOGY 



spread by a sick child before there are any signs to show that the 

 disease is anything more than a common cold. 



2. Some persons may have a disease so mildly that they do not know 

 that they have it. Diphtheria and scarlet fever are usually spread from 

 this kind of cases, for bad cases usually receive care. 



3. Germs of a disease may sometimes be found in the mucus and 

 folds of the nose and mouth of healthy persons who are immune, and 

 may spread from them to some one in whom they will grow. Diphtheria 

 is sometimes spread in this way. 



4. We cannot always tell how soon a person is free from all germs 

 after he has recovered from a disease. Germs of typhoid fever may re- 

 main alive in the gall bladder for years, and thus a person who seems 

 entirely recovered from the disease may be the means of its spread to 

 others. 



727. Fever. While an infectious disease is coming on, 

 the body can throw off the toxins as fast as they are pro- 

 duced. When the germs have multiplied enormously, 

 some of the poisonous toxins will be retained in the body, 

 and then the disease suddenly develops. The toxins pro- 

 duce a headache and a great weakness of the whole body, 

 and cause the heart beats to become weak and rapid. 

 But the principal sign of an infectious disease is usually 

 fever. A fever is seldom caused by anything else than the 

 poisons of disease germs which are growing in the body. 

 The poisons, and not the increased heat of the body, are 

 what make a fever dangerous. We can easily lower the 

 temperature of a feverish person, but it does little good 

 ^unless we also get rid of some of the poisons which cause 

 the fever (p. 263). 



728. Cause of Colds. The most common infectious 

 diseases are what are called colds. Colds are caused by 

 several kinds of disease germs which grow in the mucous 

 membrane of the nose and throat. The sickness usually 

 comes on after some part of the body has been wet or 

 chilled, but dampness and cold drafts do not make us take 



