Biological Therapy 



109 



producing anti-hog cholera serum.) These immune sera 

 contain the desired antibodies which, when injected into 

 animals, mechanically protect them against specific infec- 

 tion or combat infection already present, without any asso- 

 ciated stimulation of the body cells. It is for this reason 

 that immune sera are so valuable for combatting disease in 

 individuals already infected without the associated delay 

 and reaction necessary for immunity following the injec- 

 tion of antigens. Unfortunately the immunity conferred by 

 such sera is of relatively short duration (a few weeks) and 

 for this reason it is advisable to use other available biologies 

 after recovery in order that the passive immunity may be 

 made active. 



Active Acquired Immunity. To obtain this type of im- 

 munity it is necessary that the individual establish the pro- 

 duction of antibodies within its own system. This is accom- 

 plished by the injection of an antigen which is capable of 

 stimulating the body cells to produce the desired antibodies. 

 The antibodies which are capable of preventing infection or 

 combating that which already exists differ in different dis- 

 eases. In some the necessary antibodies are in the nature 

 of antitoxins whereas in others they are opsonins, precipi- 

 tins, or agglutinins. Biologies which are used to develop 

 these antibodies must be capable of stimulating that anti- 

 body which is most capable of accomplishing the desired 

 result. To accomplish this purpose a variety of biologies 

 have been developed, amongst which are: 



1. Unattenuated viruses, such as hog cholera virus 

 which, when used with anti-hog cholera serum, confers ac- 

 tive and lengthy immunity. Such a product is fully virulent 

 and should be used only in conjunction with its specific im- 

 mune serum. 



2. Attenuated bacteria or viruses. These products are 

 properly called vaccines and should not be confused ivith 

 hacterins. Well known examples of this class are black- 

 leg, anthrax, hemorrhagic septicemia and pox vaccines. 

 These products are so attenuated during their production 

 that when injected they produce only a mild attack of the 

 disease and confer immunity, the duration of which is longer 

 than that conferred by bacterins. The use of vaccines is 

 not entirely without danger on account of the unusual sus- 

 ceptibility of some individuals and the likelihood of abscess 



