458 



PATHOGENIC MICROORGANISMS 



earth of cultivated and manured fields seems to harbor tins organism 

 with especial frequency, probably because of its presence in the dejecta 

 of some of the domestic animals. 



Biological Characteristics. The bacillus of tetanus is generally de- 

 scribed as an obligatory anaerobe. While it is unquestionably true 

 that growth is ordinarily obtained only in the complete absence of 

 oxygen, various observers, notably Ferran i and 

 Belfanti, 2 have successfully habituated the bacillus 

 to aerobic conditions by the gradual increase of 

 oxygen in cultures. Habituation to aerobic condi- 

 tions has usually been accompanied by diminution 

 or loss of pathogenicity and toxin-formation. 

 Anaerobic conditions may likewise be dispensed 

 with if tetanus bacilli be grown in symbiosis with 

 some of the aerobic bacteria. The addition to 

 culture media of suitable carbohydrates, and of 

 fresh sterile liver tissue, has also been found to 

 render it less exacting as to absolute anaerobiosis. 3 



Anaerobically cultivated, Bacillus tetani grows 

 readily upon meat-infusion broth, which it clouds 

 within twenty-four to thirty-six hours. Anaerobic 

 broth cultures may be simply made by covering the 

 surface of the medium with a layer of albolin or 

 any other oil, and removing the air by boiling. 



Upon meat-infusion gelatin at 20 to 22 C. the 

 tetanus bacillus grows readily, growth becoming 

 visible during the second or third day. There is 

 slow fluidification of the gelatin. 



On agar, at 37.5 C., growth appears within forty- 

 eight hours. Colonies on agar plates present a rather 

 characteristic appearance, consisting of a compact 

 center surrounded by a loose meshwork of fine fila- 

 ments, not unlike the medusa-head appearance of subtilis colonies. 

 In agar stabs, fine radiating processes growing out in all directions 

 from the central stab tend to give the culture the appearance of a fluff 

 of cotton. Milk is a favorable culture medium and is not coagulated. 

 On potato, growth is delicate and hardly visible. 



1 Ferran, Cent. f. Bakt., xxiv, No. 1. 



2 Belfanti, Arch, per le sci. med., xvi. 



' Th. Smith, Brown, and Walker, Jour. Med. Res,, N, S,, ix, 1906. 



FIG. 97. YOUNG 

 TETANUS CULTURE 

 IN GLUCOSE AGAR. 



