526 GENERAL THERAPEUTIC MEASURES 



smallpox; (2) by injecting killed bacteria such as hemorrhagic septice- 

 mia; (3) by injecting the specific toxins of bacteria as in the production 

 of tetanus antitoxin; (4) by the injection of antitoxins or immune blood 

 serum of animals that have recovered from disease, or that have been 

 hyperimmunized by the above mentioned methods as for in^stance in the 

 prophylactic inoculation against tetanus with tetanus antitoxin. 



Animals acquire an active immunity to certain diseases when they 

 have survived a natural or modified course of the disease produced either 

 by infection with the particular germs or by inoculation with their specific 

 vaccines, bacterins, or toxins. In this case the animal produces its own 

 immunity either because it had the disease naturally or because it has been 

 intentionally and artificially produced in a changed and less severe form. 

 Artificial or intentional active immunization is ordinarily called "vacci- 

 nation." 



Passive immunity is produced by the introduction of immunizing 

 substances of an actively immune animal into another animal. This im- 

 munity is usually conferred by the injection of blood-serum from immu- 

 nized animals, such serum carrying with it certain substances by which 

 protection is conferred. The immunizing substances of an actively im- 

 munized or a hyperimmxinized animal are known as immune bodies or 

 "antibodies." They comprise two classes: those acting on bacteria are 

 antibacterial, as for instance anti white scours serum, anti anthrax serum ; 

 while those acting on toxins are called antitoxic, as for instance tetanus 

 antitoxin. 



Active immunity develops onlj' after one or two weeks, while passive 

 immunity is established immediately after the inoculation, but passive 

 immunity does not last and protect animals for a long period as it usually 

 disappears within one to tv/o months. This is due to the fact that just 

 as soon as the injected immune bodies are eliminated from the animal 

 organism, immunity will cease; however, in the active form, the stimula- 

 tion of the infection upon the body cells causes the continuous develop- 

 ment of antibodies (immune bodies), and, therefore, a lasting immunity 

 is produced. 



From these brief remarks it can readily be seen that the production 

 of active immunity, whenever its employment is practicable, has a great 

 advantage over passive immunity, and the tendency is to employ this 

 method whenever possible. On the other hand, it frequently becomes nec- 

 essary to employ means by which the spread of the disease can be imme- 

 diately checked, and in such instances passive immunity has the advan- 

 tage over active immunity, inasmuch as it affords the animal immediate 

 protection against infection (in many instances, it exerts also a curative 

 action). Frequently, however, both methods are used as a combined in- 

 oculation by which the animal is given immediate and also lasting protec- 

 tion against an infectious disease. This form of immunization is known 

 as the "simultaneous method." This method was first employed by Lorenz 

 in swine erysipelas. Later it was employed by Kolle and Turner in 

 rinderpest, by Soberheim in anthrax, and by Dorset in hog cholera. The 

 object of the treatment is to stimulate with the material used for immuni- 

 zation, the production of apti-substances which have not e.visted rrevi- 

 ously in the body or arP^^ffWl WOT.all quantities. TlieL are 



