204 



Zielander," 1908, obtained fairly good results with Danysz virus 

 in the laboratory, also with ratin. No fixed tests were recorded. 



Rats are notoriously resistant to bacterial infection. Even plague 

 usually fails markedly to diminish their prevalence. An epizootic of 

 bacterial nature, therefore, can not be classed with the natural enemies 

 of the rat. We are not surprised, then, to learn that the bacterial 

 viruses have signally failed to accomplish their mission. 



These bacterial viruses belong to the colon-typhoid group of organ- 

 isms. They are either identical with or closely related to the original 

 bacillus of mouse typhoid discovered by Loeffler, or the paratyphoid 

 bacillus type B, which is frequently the cause of meat poisoning, or 

 the Bacillus enteritidis of Gsertner, which has been associated with 

 gastro-intestinal disorders. 



The claim that these rat viruses are harmless to man needs revision, 

 in view of the instances of sickness and death reported by various 

 observers. The pathogenicity for man depends upon the virulence of 

 the culture, the amount ingested, the nature of the medium in which 

 it grows, and many other factors. 



Danysz virus is pathogenic for rats under laboratory conditions, 

 but has feeble powers of propagating itself from rat to rat. It rapidly 

 loses its virulence, especially when exposed to hght and air. The 

 result depends largely upon the amount ingested. The other viruses 

 have proven even less satisfactory. 



Under natural conditions these rat viruses may be Hkened to a 

 chemical poison, with the great disadventage that they rapidly lose 

 their virulence and are comparatively expensive. They also have the 

 further disadvantage that chemical poisons do not possess of rendering 

 animals immune by the ingestion of amounts that are insufficient to 

 kill or by the ingestion of cultures that have lost their virulence. 



1 Zielander: Der Rattenbacillus als Batten vertilgungamittel. Arb. a. d. k. Gesnd- 

 htsmte., Berl., vol. 28, 1908, p. 145. 



