OVERCOMING INFECTION 229 



in with food have only the lining of the alimentary tract 

 between them and the body substance. Abrasions or in- 

 flammations of any of these surfaces may afford just the 

 needed portal of entry for virulent disease-producing or- 

 ganisms. One of the reasons why common colds are so 

 frequently followed by more serious infections is that the 

 irritation of the mucous membranes brought about by the 

 cold makes the membranes easily penetrable by other 

 more dangerous organisms. 



The Overcoming of Infection. — After the organ- 

 ism has passed the barrier of the body surface and estab- 

 lished itself in a favorable location among the tissues, 

 the necessary conditions for rapid growth and multiplica- 

 tion with the accompanying development of disease would 

 seem to be present. There exist, however, certain 

 mechanisms in the body which oppose the active growth 

 of the invading microbes. If these mechanisms are wholly 

 successful the organisms are destroyed before any chance 

 to multiply is afforded, and so the infection does not 

 even get started. If the resistance of the body is less 

 prompt, and yet reasonably effective, the organisms multi- 

 ply for a time, producing and pouring out their poisons, 

 and so the symptoms of acute disease appear. Presently, 

 however, the body rallies its mechanisms of defense, coun- 

 teracts the poisons, and destroys the organisms, and thus 

 recovers completely. In still other cases, either on ac- 

 count of exceptional virulence on the part of the invading 

 organisms, or an inefficient defensive mechanism on the 

 part of the infected individual, the development of the 

 organisms and the production of poisons by them become 

 marked enough to destroy the life of the victim. 



The body has two distinct means which it rallies sepa- 

 rately or in cooperation in the effort to overcome infection. 

 The first of these is certain of the white blood-corpus- 

 cles, to which, on account of this very action, the name 

 phagocytes (scavenger cells) has been applied. The 

 second is a method by which the poisons, or the organ- . 



