DISEASE IN GENERAL 197 



that condition generally termed immunity. They consist of 

 the following: 



(1) The A ntibodies in the Blood-^plasma and Tissue-fluid.^-These 

 substances are similar in character to enzymes and appear to act 

 in a chemical manner. They are stimulated to production 

 through the introduction of foreign substances. They prevent 

 bacteria from multiplying and neutralize the poisons produced 

 by them. The majority of infections are brought under control 

 by the action of antibodies before they have done any harm and 

 while the number of infecting organisms is small. On the other 

 hand, if the invasion of bacteria is great, the antibodies are 

 not capable of overcoming them, and disease results either from 

 the mechanical interference produced by the organisms, or from 

 a poisoning of the body by the noxious bacterial toxins which 

 circulate with the blood to all parts of the body. Certain organs 

 are more susceptible to the action of these poisons than others 

 and give way to them more quickly. This is well illustrated in 

 cases of tetanus, where the organs of the- nervous system are the 

 first to show the effects of the toxin produced by the tetanus 

 bacilli. Among the most useful antibodies are antitoxins, which 

 neutralize the harmful effect of bacterial toxins; agglutinins, 

 which cause bacteria to clump or agglutinate and lose their 

 motility; precipitins, which precipitate certain organisms under 

 favorable conditions. 



The blood-plasma circulates in the blood-vessels. The tissue- 

 fluid, on the other hand, circulates about and bathes the cells of 

 the body. All substances that reach the individual cells are 

 carried by this fluid. -Besides food materials and antibodies, it 

 conveys large numbers of leukocytes. 



(2) The Leukocytes or White Blood Corpuscles. — These cells are 

 capable of passing through intact walls of the blood-vessels and 

 of migrating into the tissues. They congregate at the seat of 

 infection and destroy by an eating process the bacteria that are 

 attempting to invade the tissues. As active agents in aiding 

 the body in the fight against foreign invaders they are very im- 

 portant. Someone has truthfully called them the mobile members 

 of the body's defensive army. 



(3) The Red Blood Corpuscles. — These cells are capable of oxi- 

 dizing certain injurious substances when they come in contact 

 with them. The process of oxidation is simply the liberation 



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