554 PATHOGENIC MICROORGANISMS 



Passive immunization of animals with the serum of actively immunized 

 horses has been practiced by Kitt and Mayr,' Schreiber,^ and Wasser- 

 mann and Ostertag. The last-named observers, working with a poly- 

 valent serum produced with a number of different strains of the bacillus, 

 have obtained results of considerable practical value. The researches 

 of Kitt and Mayr have revealed a fact pointing to the interrelationship 

 of the bacilli of the "hemorrhagic septicemia" group. They were able 

 to show that the serum of horses immunized with chicken cholera 

 bacilli was able to protect, somewhat, against Bacillus suisepticus. 



Infection with the bacillus of swine plague, in hogs, is often ac- 

 companied by an infection with the hog-cholera bacillus (Schweinepest). 

 The latter, as we have seen, is a microorganism belonging to the enteri- 

 tidis group, intermediate between Bacillus coli and Bacillus typhosus, and 

 differing from suisepticus in being actively motile, possessing flagella, 

 not showing the polar staining, having a more slender morphology, and 

 producing gas upon dextrose broth. A confusion between the two 

 bacilli frequently occurs because of their nomenclature. Bacteriologic- 

 ally and pathogenically, they are quite distinct. Bacillus suisepticus 

 produces an acute septicemia, accompanied by bronchopneumonia and 

 usually not affecting the gastro-intestinal canal. The bacillus of hog 

 cholera produces an infection localized in the intestinal canal. 



BACILLUS PESTIS 



{Bacillus of Bubonic Plague) 



The history of epidemic diseases has no more terrifying chapter 

 than that of plague.^ Sweeping, time and again, over large areas of 

 the civilized world, its scope and mortality were often so great that 

 all forms of human activity were temporarily paralyzed. In the 

 reign of Justinian almost fifty per cent of the entire population of 

 the Roman Empire perished from the disease. The "Black Death" 

 which swept over Europe during the fourteenth century killed about 

 twenty-five million people. Smaller epidemics, appearing in numerous 

 parts of the world during the sixteenth, seventeenth, and eighteenth 

 centuries, ha^e claimed innumerable victims. In 1893, plague appeared 

 in Hong Kong. During the epidemic which followed, Bacillus "pestis, 

 now recognized as the etiological factor of the disease, was discovered by 



' Kitt und Mayr, Monatsh. f. prakt. Thierheilk., 8, 1897. 



'Schreiber, Berl. tierarztl. Woch., 10, 1899. 



3 Hirsch, " Handb. d. histor.-geogr. Path.," 1881. 



