BA CTERIOL YSINS A ND H^EMOL YSINS 113 



timing the injections an animal may be made to pro- 

 duce sufficient anti-substances to combine with many 

 times the amount of the substance introduced. 



The production of antibodies by an inoculated 

 animal is well shown when a horse is immunized to 

 the gonococcus by the injection of this organism. 

 Although all the body fluids of an inoculated animal 

 may contain anti-bodies the blood serum is spe- 

 cially rich in them and, therefore, the serum is most 

 frequently used to demonstrate their presence. All 

 substances which are used to cause an animal to 

 produce antibodies are called antigens, and some of 

 the bacterial antigens in daily use are the gonococ- 

 cus, streptococcus, meningococcus, etc. The blood 

 serum of an animal which has been inoculated with 

 any antigen and which, therefore, contains anti- 

 bodies, is called an anti-serum and corresponding 

 to the above antigens there are anti-gonococcus, 

 anti-streptococcus, anti-meningococcus sera, etc. 

 These so-called antibodies are present in the blood 

 of animals which have accidentally become infected 

 just as well as in the blood of animals which have 

 been experimentally inoculated. Hence when one 

 desires to ascertain whether or not an animal has 

 become infected and, if so, by what organism, it is 

 only necessary to test for the corresponding anti- 

 bodies. The antibodies produced as a result of the 

 presence of an antigen will combine with that antigen 

 and this combination will take place in a test-tube. 



