CHAPTER XLVIII 



DEFENSES 

 AGAINST DISEASE 



iti r„1,ii,M'-r,fii Mil .M.,,-:,,,,,! ri 



t T ^ 



anbi-bpacirz-. 



The scavengers of the body. 



Antitoxins neutralize toxins. 



How is the body 'protected against bacteria f Are the protections 

 adequate? Under tchat conditions are the defenses inadequate? 



Diseases of the bodv mav be due to dandular disturbances 

 such as cretinism ; inadequate diets, as rickets ; constitutional 

 tendencies or disturbances ; or to infections from microorganisms. 

 Parasitic microorganisms exist in great numbers, but most of 

 them are either kept out of the body or destroyed when they enter 

 the body. There are comparatively few diseases caused by bac- 

 teria when compared with the existing number of parasitic 

 bacteria. 



Behavior of bacteria in the body. Bacteria have different 

 modes of attack and different ways of breaking through the de- 

 fenses of the bodv. Some bacteria actuallv destroy tissue. For 

 example, the tuberculosis bacillus devours various tissue cells, 

 and thus destroys them. It is thought that certain parasitic bac- 

 teria which cause boils and abscesses send out enzymes which 

 dissolve the white blood cells so that they can be absorbed by 

 the bacteria. The pus formed in boils and abscesses is dead white 

 corpuscles. Other bacteria act on the body chiefly through the 

 toxins or exotoxins they produce. These pass into the tissues 

 surrounding the bacteria, get into the blood, and circulate through 



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