BACILLUS MUCOSUS CAPSULATUS 723 



spores, are characteristics common to all. In size, general appear- 

 ance, gas formation, and pathogenicity, individual strains may vary 

 much, one from the other. Strong 4 has studied various races as 

 to gas formation and concludes that most strains form gas from 

 dextrose and levulose, but that lactose is fermented by some only. 

 About two-thirds of the gas formed is hydrogen, the rest C0 2 . Acid 

 formation, according to Strong, is also subject to much variation 

 among different races. Similar studies by Perkins 5 show that most 

 of the ordinary cultural characteristics of bacilli of this group are 

 extremely variable and can not serve as a basis for differentiation. 

 Reactions on sugars, however, are more constant. Perkins suggests 

 the following tentative division classes on this basis: 



I. All carbohydrates fermented with the formation of gas. 



II. All carbohydrates, except lactose, fermented with the forma- 

 tion of gas. 



III. All carbohydrates, except saccharose, fermented with the 

 formation of gas. 



Type I. corresponds to B. aerogenes (Migula), type II. to B. 

 Friedlander or Bacterium pneumoniae (Migula), and type III. to 

 Bacillus lactis aerogenes. 



Differentiation by means of serum reactions has not proved satis- 

 factory. 6 



Pathogenicity. When Friedlander first described this micro- 

 organism, he assumed it to be the incitant of lobar pneumonia. Sub- 

 sequent researches by Weichselbaum 7 and others have shown it to 

 be etiologically associated with pneumonia in about seven or eight 

 per cent of all cases. The percentage in this country is probably 

 lower. Such cases can often be diagnosed by the presence of the 

 bacilli in the sputum, which is peculiarly sticky and stringy. Cases 



4 Strong, Cent, f . Bakt., xxv, 1899. 



5 Perkins, Jour. of. Infect. Dis., I, No. 2, 1904. 



6 J. G. Fitzgerald, who has recently made a careful study of the mucosus cap- 

 sulatus group has concluded that present methods do not permit a subdivision of 

 these organisms into separate species. He offers the following "tentative sug- 

 gestion": "It is conceivable that mutations based on the necessity of maintaining a 

 parasitic existence have caused Gram-negative bacilli found normally in the body 

 elsewhere than in the intestinal tract to develop capsules for protection and a new 

 group has arisen which we designate B. mucosus capsulatus; and the varieties B. 

 aerogenes and B. acidi lactici connect the group with the non-encapsulated colon 

 group." 



7 Weichselbaum, loc. cit. 



