84 VETERINARY PADIOLOGY. 



0. 



By simultaneous inoculation with a virus and an antitoxin 

 (antibodies, bactericidal substances, etc.) In the Philippine 

 Islands this method is employed in immunizing cattle against 

 rinderpest, and it is also being successfully used in the immun- 

 ization of hogs, against cholera. 



Toxic imnuKiitv is the resistance to poisonous substances as 

 toxins of bacterial origin, zootoxins and phytotoxins. It is 

 common to hear sheep herders speak of dogs that are immune 

 til the venom of rattlesnakes. The dogs are bitten frecpiently 

 wliile doing dut^- on the range and although the reactinn from 

 the first inoculation is intense and mav even kill, each succeed- 

 ing inoculation produces less reaction until finally the diigs may 

 be bitten or the ^-cnom inoculated with impunity. Immunity to 

 intoxication diseases such as tetanus are of this t}-pe. The ab- 

 sence of action of various therapeutic agents that have been 

 gix'cn repeatcdK- mav be explained on the principles similar lo 

 those inv'lved in the production of immunity in dogs to snake 

 \-enom. Toxic immunity- is tlie result of the presence in tiie 

 bndv fluids of an antibod^• (Antitoxin.) 



Bacterial immunity is the resistance an infected animal 

 manifests to the bacterial in^•ader. It is the result of bacteri- 

 (ilvtic substances in the bodv fluids. Pfeiffer demonstrated that 

 bacteria are destroyed when introduced into an immune animal. 

 He introduced the spirilla of Asiatic cholera into the peritfineal 

 cavity of guinea pigs and nuted that the liacteria were soon 

 rendered immobile, became swollen and granular and were fin- 

 alU' disintegrated. This phenomena has been designated Pfeif- 

 fer's reaction. 



Passi?'C acquired immunity consists essentially of the jiresence 

 in the tissues or l)ody fluids of substances inimical to micro- 

 parasitic activity, or substances capable of union with micro- 

 parasitic products, (toxins) thus rendering them inert. This 

 type of immunitv is of short duration. It is usually produced 

 b}- the inoculation of susceptible animals with antitoxin. Injured 

 animals inoculated with tetanus antitoxin at the time of injury 

 are thus immunized to tetanus for a brief period. 



Acquired immunity, like natural immunity, is variable and 

 inconstant. The production of active acquired immunitv entails 

 more risk than the production of passive acquired immunitv. 

 The causative agents or their toxic products are used in obtain- 

 ing an active immunity and thus disease may be produced and 

 the animal life sacrificed while the anti-toxin is used in the 

 production of a passive immunity, without danger of the pro- 

 duction of disease although transient disturbances mav result 



