IMMUNITY AGAINST PURE PARASITE. 39 



Bail places the utmost stress upon the difference between an immunity 

 directed against the exciting agent of the disease (bactericidal immunity) and 

 that against the disease itself (anti-aggressive immunity) . 



Immunization against the disease is only possible if the aggressin reaches the body 

 of the animal to be immunized. This is possible either by employing Pasteur's method 

 of vaccine inoculation, i.e., the injection of bacteria, the " aggressive" nature of which 

 has been weakened but not destroyed, or by direct inoculations of aggressins. The 

 latter is by far the simpler and more reliable mode of procedure, being productive of 

 a true immunity. 



Nowhere does this problem appear of such extreme importance as where 

 immunity against a pure parasite is contemplated as in the 

 Immunity case f swine pest and chicken cholera. While it is exceed- 

 Against Pure ingly difficult, in fact almost impossible to immunize against 

 Parasite, these bacteria either with dead or living germs or vaccines, 

 this task is readily accomplished by the injection of non- 

 poisonous aggressins, inasmuch as they are well tolerated. In addition 

 these bacteria are of help in definitely deciding whether or not an aggressin 

 immunity is at all possible. 



Weil, a co-worker of Bail's, has carried out these experiments for chicken 

 cholera, while the author has done the same for swine pest. 



Example of Active Immunization with Natural Aggressins. 



a. Slow Immunization. 



Rabbit I. 



6./IV. 1905 ist injection: i.o c.cm. natural swine pest aggressin intraperitoneally. 

 17. /TV. 2d injection: i.o c.cm. natural swine pest aggressin intraperitoneally. 



25. /TV. 3d injection: i.o c.cm. natural swine pest aggressin intraperitoneally. 



i./V. 4th injection: 2.0 c.cm. natural swine pest aggressin subcutaneously. 



12. /V. 5th injection: 2.0 c.cm. natural swine pest aggressin subcutaneously. 



i6./VI. ist infection; with i/ioo loopful of swine pest culture intravenously. 



17. /VI. Perfectly well. 



8./VII. 2d infection; with i loopful of swine pest culture intravenously. 



I5./VII. Perfectly well. 



22. /IX. 3d infection; with i loopful of swine pest culture intravenously. 



3-/X. Perfectly well. 



Rabbit I. Controls. Rabbit II. 



i6./VL 1905 1/100,000 loopful of swine 

 pest culture intra- 

 venously. 



I7-/VI. t found dead. 



8./VII. 1905 1/10,000 loopful of swine 

 pest culture subcutan- 

 eously. 



9./VII. f found dead. 



