HOW BACTERIA CAUSE DISEASE 261 



on which the bacteria Hve, and cause the symptoms of certain 

 diseases. Each species of bacteria forms its own specific toxin, 

 and this has a specific action on the body, causing the symptoms 

 of a specific disease. As bacteria can multiply rapidly in the body, 

 they may become very numerous before the body defenses (see 

 page 168) gain control of the situation. When the bacteria die, 

 as they may in great numbers during the progress of the disease, 

 their bodies break down, and the released protoplasmic constitu- 

 ents, particularly the proteins, separate from each other and split 

 into smaller and smaller molecular groups, as do the proteins when 

 changed to amino-acids during digestion. These split proteins, as 

 they are called, are extremely poisonous to the body tissues and 

 act as toxins in the body, causing many of the characteristic 

 symptoms of disease. 



Some bacteria break down the body tissues, besides producing 

 toxins. They may destroy the intestinal lining, or destroy the 

 blood corpuscles, or break down tissues in wounds, thus causing 

 specific symptoms of disease. 



It is estimated that germ diseases cause annually over 50 per 

 cent of the deaths of the human race. A very large proportion 

 of these diseases might be prevented if people were educated 

 sufficiently to take the proper precautions to prevent the spreading 

 of bacteria. These precautions might save the lives of some 

 3,000,000 people yearly in Europe and America. Tuberculosis, 

 typhoid fever, bubonic plague, diphtheria, pneumonia, blood 

 poisoning, and a score of other germ diseases ought not to exist. 

 A good deal of the present misery of this world might be prevented 

 and this earth made cleaner and better by the cooperation of young 

 people now growing up to be our future home makers. 



How we get Germ Diseases. — Germ or infectious diseases 

 enter the body either by way of the mouth, nose, or other body 

 openings, or through a break in the skin. They may be carried 

 by means of air, food, or water^ but are more often transmitted 

 directly from the person who has the disease to a well person. 

 They may be acquired through personal contact ; from the mouth 

 spray of persons who have certain diseases ; by handling or using 

 articles, such as towels, handkerchiefs, cups, or dishes used by 

 sick persons ; or by drinking or eating foods which have received 



H. NEW CIV. BIOL. — 18 



