548 PATHOGENIC BACTERIA. 



tents, and Kitt, who discovered them in this position, 

 points out that the infection of swine probably takes 

 place by the entrance, along with the food, of the fecal 

 matter of diseased animals into the alimentary apparatus 

 of others. 



Pasteur, Chamberland, Roux, and others have worked 

 upon a protective vaccination based upon the attenuation 

 of the virulence of the organism by passing it through 

 rabbits. Two vaccinations are said to be necessary to 

 produce immunity. The vaccinated animals, however, 

 may be a source of infection to others, and should always 

 be isolated. ' Klemperer in 1892 found that the blood- 

 serum of immunized rabbits would save infected mice 

 into which it was injected. 



Lorenz in 1894 found an antitoxic substance in the 

 blood of rabbits immunized to the disease. The effect 

 of its injection into other animals is, however, only a 

 temporary immunity. Later 1 he found it possible to 

 protect hogs against the disease by injecting them first 

 with a serum obtained from a hog immunized in the 

 ordinary manner described by Pasteur, afterward with 

 a feeble culture of the bacillus, and finally with viru- 

 lent cultures. The strength of the serum should be 

 determined by injecting varying quantities of it into 

 mice infected with definite amounts of a culture of 

 known virulence. The immunity produced by Lorenz 

 lasted for a year. 



1 Centralbl.f. Bakt. u. Parasitenk., Jan., 1896, p. 168. 



