AEROBIC SPORE-BEARING NON-PATHOGENIC BACTERIA 299 



end of the rods which do not swell appreciably. When free 

 they may retain spurs of protoplasm at each end unequal in 

 quantity and measure about 0.5 by 1.5 microns. The spores 

 rapidly lose their rims of protoplasm and are then oval to cylin- 

 drical measm'ing 0.5 by 0.75 microns. 



Motility. Actively motile in 24 hour cultures. 



Staining properties. Gram-positive. 



Cultural reactions. This organism is identical with Bacillus 

 vulgatus in all its cultural reactions except that it imparts a dis- 

 tinct color to the various media. This color varies from a steel 

 grey to a brown or black and is best seen on solid media. It is 

 very pronounced on potato where the characteristic folds of the 

 "vulgatus" are converted to thick black wrinkhng bands. 



Thermal death point. The spores resist an hour's steaming in 

 the Arnold sterihzer and 15 pounds pressure in the autoclave. 

 They are destroyed by 16 pounds pressure. 



Bacillus niger Migula 1900 



This organism was first described by Gorini (1894) in 1894 as 

 Bacillus lactis-niger and is closely related to the preceding 

 organism. A culture obtained from Krai's Laboratory shows 

 the following reactions. 



Morphology. Bacilli with homogeneous protoplasm and blunt 

 or rounded ends measuring 0.375 to 0.75 by 1.5 to 3 microns in 

 24 hour agar cultures. No change in morphology on glucose agar. 

 (Figures 12 and 13.) 



Spore formation. Spores are formed in 24 hours on plain agar 

 and in 48 hours on glucose agar. They appear in the center or 

 towards one end of the rods and are oval or cylindrical in shape. 

 The free spores may retain protoplasm at both ends and are 

 typical of the ^'mesentericus" group. They measure 0.75 to 1 

 by 1.125 to 1.25 microns in dimensions. 



Motility. Active motihty in young cultures. 



Staining properties. Gram-positive. 



Cultural reactions. This species has the general cultural 

 reactions of Baciltus mesentericus. It grows on agar as a rather 



