Immunity may also be induced artificially, as in vaccination, by introducing 

 substances that stimulate the blood to actiue production of specific anti- 

 bodies. 



The specific reaction of the body, particularly the blood, to foreign sub- 

 stances makes it possible to recognize, or diagnose, specific diseases and to 

 discover specific immunities and sensitivities by means of serums. 



The discovery of serum reactions in the last decade of the past century 

 led to far-reaching changes in the treatment and prevention of communi- 

 cable diseases, making it possible practically to exterminate some diseases. 



EXPLORATIONS AND PROJECTS 



1 To demonstrate the extent of regeneration in flatworms (planarians), cut 

 several well-fed worms into two, three or four pieces.^ Observe them frequently 

 for two weeks to see the extent to which lost parts are regrown. 



2 To ascertain whether members of the class are susceptible to diphtheria, 

 arrange with the school nurse or doctor to have each one given the Schick test. 

 What connection is there between susceptibility and age, sex, previous illnesses, 

 general health, vaccinations in the past? 



3 To find out about the diagnostic tests used in safeguarding the health of 

 the residents of your community, visit the health department and gather informa- 

 tion about its activities. 



QUESTIONS 



1 How does a wound heal? 



2 How do organisms regenerate lost organs? 



3 In what different ways do poisons affect the body? 



4 How does the action of habit-forming drugs differ from that of other 

 drugs or poisons? 



5 How do antitoxins differ from serum preparations? 



6 What is immunity? In what different ways can immunity be acquired or 

 induced ? 



7 Why is it that an active immunity is much more lasting than a passive 

 immunity ? 



8 What kinds of substances are produced by the body which tend to make 

 it immune to different foreign substances or diseases? 



9 Why are the various immunizing serums prepared from several different 

 animals? 



^Keep flatworms in shallow glass dishes. Feed fresh liver every day or so. Change water 

 a half-hour after each feeding to remove liver not eaten. 



246 



