CHAPTER III. 



ACTIVE IMMUNIZATION. 



IMMUNIZATION WITH LIVING AND DEAD VIRUS. 



Active immunization depends upon the principle, that an organism in 

 overcoming a slight infection, either naturally or artificially 



ncip e acquired, develops enough protective bodies to withstand a 

 of Active . ., . , . , ^. 



Immun- similar, severer, natural, or acquired infection. Moreover, 



ization. ^ serves primarily the purpose of prophylaxis. In labora- 

 tories, active immunization of animals is also frequently under- 

 taken with the view of obtaining sera for diagnostic and therapeutic 

 purposes. 



In the manufacture of large quantities of serum, the horse is the animal 

 used almost exclusively. Occasionally cows, sheep, donkeys or mules' 

 are selected. In small laboratories usually rabbits, guinea-pigs, white 

 mice, rats, and only occasionally goats or sheep are employed. 



The process of immunization evokes a marked disturbance in the gen- 

 eral health of the animals. For this reason they must be well kept in 

 warm places, and well fed. As far as their power of producing antibodies 

 is concerned, there are individual differences even among the same species 

 of animals; thus if five horses are immunized against diphtheria, some will 

 give much better curative sera than the others. In general, the younger 

 animals are preferable. 



Any substance which, when injected into an organism, can stimu- 

 late the production or formation of antibodies, has been conveniently 

 termed " antigen." After the injection of such an antigen, special notice 

 should be taken of the animal in reference to temperature, weight, the 

 excitation of diarrhea or the occurrence of abscesses, infiltrates, edema 

 or paralysis. 



If an animal dies, a careful postmortem, and if possible, a bacteriolog- 

 ical examination should be made. It should be the aim to ascertain if death 

 was induced by the inoculated antigen, by contamination or secondary 

 infection. One should always keep in mind the possibility of some of the 

 animal epidemic diseases. 



Epidemic diseases occurring in rabbits are: 



Animal i. RABBIT SEPSIS. Presents itself in the form of bronchopneumonia and 

 Infections, marked nasal catarrh. It is very infectious. Sick animals should at 

 once be isolated or killed and their cages thoroughly disinfected. 



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