CHAPTER 1 

 Antibodies I 



Immunity 



Basically speaking, immunity is the increased resistance to an in- 

 fectious disease which often follows recovery from an initial attack. 

 The degree of this immunity is different with different diseases and 

 different patients and persists for varying periods of time. Recovery 

 from certain virus diseases, such as yellow fever, is followed by a 

 very high degree of resistance which seems to last for life in many 

 patients. Recovery from the common cold, on the other hand, is 

 followed by a very brief state of increased resistance, if indeed by 

 any at all. We shall also apply the term immunity to the artificially 

 increased resistance produced in a patient by injection or oral ad- 

 ministration of living virus or living microorganisms or by injection 

 of attenuated or dead virus or microorganisms or of antigenic prod- 

 ucts derived from such material. A patient whose resistance has been 

 heightened by such treatment is said to have been immunized, al- 

 though he may not be immune in the absolute sense of the word. 

 Animals which have been caused to produce antibodies by such ad- 

 ministration of antigen are also said to have been immunized, even 

 though they may not have obtained increased resistance to any 

 disease as a result. 



Role of Antibodies in Imuinnity 



The circulation of the immune animal often contains soluble pro- 

 tective proteins called antibodies, a term which is also applied to 

 specifically reactive proteins produced in response to any antigen, 

 whether it is derived from a pathogenic microorganism or not. 



