GENUS BACTERIUM 297 



toxins is, when injected into their bodies, pathogenic for 

 guinea pigs, rabbits, chickens, pigeons, small birds, and cats; 

 also in a lesser degree for dogs, goats, cattle, and horses, but 

 hardly at all for rats and mice. In spite of its pathogenic 

 qualities for these animals true diphtheria occurs in them 

 with extreme rarity. As a rule, so called diphtheritic inflam- 

 mations that occur in these animals are due to other bacteria. 

 According to Park, the cat is the only animal that has been 

 known to contract true diphtheria. 



Bacteria closely resembling Bact. diphtheriae. Bacillus 

 Hoffmanni (Pseudodiphtheria bacillus). Hoffmann-Wellen- 

 hoff 12 in 1888, and, at almost the same time, Loeffler 13 de- 

 scribed bacilli which they had cultivated from the throats of 

 normal individuals and in several instances from those of 

 diphtheritic persons, which were in many respects similar to 

 true Bact. diphtheriae, but differed from it chiefly in being 

 non-pathogenic for guinea pigs. These organisms were at 

 flrst regarded by some observers as merely attenuated diph- 

 theria bacteria. More recent investigations, however, proved 

 them to be unquestionably a separate species, easily differen- 

 tiated by proper methods. They differ from Bact. diphtheriae 

 in so many important features that the term "pseudo-diph- 

 theria bacillus" is hardly an appropriate one for them. Dif- 

 ferentiation can finally be made on the basis of animal 

 pathogenicity, B. Hoffmanni being entirely innocuous to the 

 ordinary laboratory animals. B. Hoffmanni forms no toxins, 

 and animals immunized with it do not possess increased re- 

 sistance to Bact. diphtheriae. The pseudo diphtheria bacteria 

 do not, according to Smith, 14 produce acids in bouillon con- 

 taining dextrose. 



Many bacilli have been described which have a slight 

 morphological resemblance to the diphtheria organism but 

 which have little or no pathological significance. Such or- 

 ganisms are met with in milk, air, and water, and as secondary 



12 lloffmann-Wellenhoff. Wien. Med. Woch., Bd. Ill (1888). 



13 Loeffler. Centralbl. f. Bakt, Bd. II (1887) p. 524. 



14 Smith. 28th Annual Report State Bd. Health, Mass., 1897. 



