284 HEALTH AND DISEASE 



within it. For example, the special bacterium of pneu- 

 monia is found in almost every one's mouth, where it 

 remains as a harmless parasite, totally unable to force 

 an entrance into the body because of the vigilance of 

 the white blood corpuscles. When, however, through 

 extreme fatigue or a severe chill, the power of the blood 

 corpuscles is greatly reduced, the bacteria find their 

 entrance but weakly contested by them and so are able 

 to enter and multiply. The result of their activity 

 is the disease of the lungs known as pneumonia. 



Generation of toxins. Like all unicellular organ- 

 isms, microbes multiply by division. The process of 

 division goes on so rapidly that under favorable cir- 

 cumstances one microbe requires but a few hours to 

 become millions. As they increase in numbers, they 

 generate the most active poisons known, the toxins. 

 These poisons are absorbed by the lymph and carried 

 all over the body, with the result that the body is 

 prostrated. 



Antibodies. In spite of its prostration, the body sets 

 about to resist the poison of the infecting microbes. It 

 is stimulated to increased activity by the toxins, as 

 shown by the fever which is the usual accompaniment 

 of disease. As a result of this activity, there is devel- 

 oped a substance called antibody or antitoxin, which has 

 a threefold power. It neutralizes the poisonous effect 

 of the toxin; it weakens the invading organisms; and 

 it stimulates the white blood corpuscles to destroy them 

 more actively. If the body is able quickly to develop 

 a large amount of antibody, the disease runs an un- 

 usually short course and is said to be aborted. If, on 

 the contrary, the infecting microbes are of overwhelming 

 strength and numbers, the body has little or no chance 

 to develop an antibody before it is overcome by the 



