Immunization. 2^37 



and in ease the protection is not sufficient the animals may be revac- 

 cinated shortly before weaning with the bacterial extract. 



2. Serum Immunization. Blood serum from animals treated 

 with virulent cultures of the bacillus suisepticus protects test 

 animals for a short time against a subsequent virulent infection. 

 As a result of these experimental findings serum of horses 

 hyperimmunized by subcutaneous and intravenous injection of 

 increasing doses of virus has been used in numerous instances 

 for the immunization of hogs (see also page 141). 



Schweinitz had already in 1890 immunized horses, mules and cattle 

 with either living or dead cultures, as well as with filtrates, and also 

 with toxic substances isolated from cultures. He proved that the serum 

 of such immunized animals afforded a protective action against an 

 infection with the bacillus suisepticus or against the action of its 

 toxins. The serum was usually employed together with the hog cholera 

 serum against the mixed infection, which occurs in America, but with 

 doubtful results. 



Later Schreiber obtained an immune serum from horses treated 

 with cultures, which was placed on the German market under the name 

 " Septizidin. " According to his views his product possesses both a 

 protective and also a curative action, and is often used against the 

 septic pneumonia of calves. 



Polyvalent immune serum. According to Wassermann & Ostertag 

 blood serum of artificially immunized animals usually protects only 

 against the variety of the bacillus suisepticus which had been used for 

 the immunization. On the other hand its action against the otlier 

 varieties of this organism is ineffective in spite of the fact that morpho- 

 logically and in their cultural characteristics they are identical. Ac- 

 cording to their conception the protoplasm of the bacterial cell consists 

 of different components which, in the different varieties of the same 

 bacterium, are to some extent not identical. Besides a common domi- 

 mant receptor which is to be considered as the carrier of the special 

 characteristics of the species of bacteria, the different varieties may 

 contain individually different side-receptors. Inasmuch as during the 

 process of immunization the various components produce corresponding 

 immune bodies (amboceptors) by binding the receptors adapted to them 

 (Ehrlich's theory), all these immune bodies bind the dominant re- 

 ceptor; but the side-receptors of the variety which have been used 

 for the immunization, thereby afford a protection only against the 

 latter, and are ineffective against varieties containing other side- 

 receptors. The above mentioned authors accordingly treated horses 

 with as many varieties as possible of the bacillus suisepticus and found 

 that the serum proved effective against all the different varieties. This 

 polyvalent or multipartial serum with a titre of not less than 0.01 cc. 

 for mice against a dose ten times the fatal dose of a living culture 

 has been used especially against the pneumonia of pigs. 



Immunization with chicken cholera sernm. Klett & Braim employ serum of 

 horses which have been treated for a long period with a mxiture of toxins from 

 killed cultures and their filtrates, and which afterward have been inoculated with 

 fully virulent chicken cholera bacteria. These authors contend that the bacilli of 

 fowl cholera produce the same toxin, only in larger quantities, as the bacilli of 

 swine plague. Serum from horses treated in the above manner protects gray mice, 

 in quantities of 0.0015-0.005 gm., against a fatal infection of a loopful of virulent 



