226 GENERAL THERAPEUTICS FOR VETERINARIANS 



immunity, which is also called inherited immunity. It is due to 

 an inherited special property of the body cells and the blood 

 which cannot be transmitted to other animal species. An acquired 

 immunity, on the other hand, is established after an animal has 

 passed through a single attack of a certain disease and lasts for a 

 certain time (immunity after recovery). This variety of immunity 

 may follow an attack of pox, anthrax, lung plague, foot-and-mouth 

 disease, strangles, canine distemper, black leg, swine erysipelas, 

 etc., and also scarlet fever, measles, typhoid fever and diphtheria 

 of man. 



The acquired immunity is to be attributed to the presence of 

 specific substances in the body (blood, blood-serum) which reduce 

 the susceptibihty of the organism to the infectious agents which 

 caused the disease. These immunizing substances either neutral- 

 ize the toxins formed by the invading bacteria (antitoxic action, 

 toxic immunity) or they destroy the pathogenic bacteria them- 

 selves (bactericidal action, bacterial immunity). In contrast to 

 natural immunity, acquired immunity may be transmitted from 

 one ammal species to another (pox from cattle to man). 



Finally, two varieties of acquired immunity are recognized, 

 the active and the passive. The active immunity is acquired 

 spontaneously by an animal in passing through an attack of the 

 particular disease (natural or artificial infection). This immunity 

 can be increased by a repetition of the infection and can usually 

 be made more continuous. It is due to the formation in the blood- 

 serum of antibodies (antitoxins, bacteriolysins, bactericides). The 

 passive immunity is produced by the artificial introduction of the 

 antitoxins (secondary immunity). It is only of short duration 

 because the antibodies artificially introduced are soon used and 

 none are formed to replace them, as occurs in active immunity 

 (inoculation of blood-serum in contagious pneumonia of horses, 

 foot-and-mouth disease, rinderpest, and swine erysipelas) . In vacci- 

 nation against swine erysipelas the swine are passively 

 (serum inoculation) as well as actively (inoculation of bacilli) 

 immunized. 



