THE HIGHER BACTERIA 



621 



organisms seem to indicate that not all of the incitants described be- 

 longed to one and the same variety, but that probably a number of 

 different types may exist. 



Morphology. Morphologically the streptothrices show considerable 

 variation. In material from infectious lesions they have most often 

 appeared as rods and filaments with well-marked branching. Occasion- 

 ally the filaments are long and interwined, and branches have shown 

 bulbous or club-shaped ends. In Norris and Larkin's case, the young 

 cultures in the first generations seem to have consisted chiefly of rod- 

 shaped forms not unlike bacilli of the diphtheria group, showing marked 

 metachromatisir when stained with Loeffler's methylene-blue. They are 



FIG. 140. STKEPTOTHRIX, SHOWING TRUE BRANCHING. 



easily stained with this dye or with aqueous fuchsin. In tissue sections 

 they may be demonstrated by the Gram-Weigert method. 



Cultivation. Direct cultivation upon agar and gelatin plates has 

 occasionally been successful. At the end of four or five days grayish- 

 white, glistening, flat colonies may appear which attain a diameter of 

 several millimeters within two weeks. The coloni later may take on a 

 yellowish hue and begin to liquefy the gelatin. In bouillon flocculent 

 precipitates and surface pellicles of interwined threads may form, with- 

 out clouding of the medium. Norris and Larkin 1 found much difficulty 

 in cultivating, but finally succeeded by making smears of the infectious 

 material upon fresh, sterile kidney-tissue of rabbits. The micro- 



1 Norris and Larkin, loc. cit. 



