784 PATHOGENIC MICROORGANISMS 



Pasteur's method has given excellent results and confers an 

 immunity which lasts about a year. 



Chauveau 20 has modified Pasteur 's method by growing the bacilli 

 in bouillon at 38 to 39 C., at a pressure of eight atmospheres. 

 Cultures are then made of races attenuated in this way, upon chicken 

 bouillon and allowed to develop for thirty days. Single injections 

 of 0.1 c.c. each of such cultures are said to protect cattle. 



Active immunization of small laboratory animals is very difficult, 

 but can be accomplished by careful treatment with extremely at- 

 tenuated cultures. 



Passive immunization by means of the serum of actively immune 

 animals was first successfully accomplished by Sclavo. 21 



The subject of passive immunization has been especially inves- 

 tigated and practically applied by Sobernheim. 22 The serum used 

 is produced by actively immunizing sheep. It is necessary to carry 

 immunization to an extremely high degree in order to obtain any 

 appreciable protective power in the serum. This is accomplished 

 by preliminary treatment with Pasteur's or other attenuated vac- 

 cines, followed by gradually increasing doses of fully virulent cul- 

 tures. Treatment continued at intervals of two weeks, for two or 

 three months, usually produces an effective serum. Horses and 

 cattle may also be used for the process, but they are believed by 

 Sobernheim to give less active sera than sheep. Bleeding is done 

 about three 1 weeks after the last injection. The sera are stable and 

 easily preserved. 



Injections of 20 to 25 c.c. of such a serum have been found to 

 protect animals effectually from anthrax and to confer an immunity 

 lasting often as long as two months. Animals already infected are 

 said to be saved by treatment with 25 to 100 c.c. of the serum. 



Neither specific bactericidal nor bacteriolytic properties have, 

 so far, been demonstrated in these immune sera. In fact, these 

 properties are distinctly more pronounced against Bacillus anthracis 

 in the normal sera of rats and dogs. Agglutinins have not been 

 satisfactorily demonstrated in sera, partly because of the great 

 technical difficulties encountered in the active chain-formation of 

 the bacillus in fluid media. An increase of opsonic power of such 



20 Chauveau, Comptos rend, de 1'acad. des sci., 1884. 



21 Sclavo, Cent, f . Bakt., xviii, 1895. 



22 Sobernheim, Zeit. f. Hyg., xxv, 1897; xxxi, 1899. 



