TEXT-BOOK OF BACTERIOLOGY. 195 



pear under the microscope as finely-granulated, yellowish- red discs 

 with smooth edges. 



In the test-tube culture thickly- crowded, roundish grains grad- 

 ually form along the puncture, which in the deeper parts take a 

 beautiful wine-red color, while in the upper part, near the top of the 

 puncture, they remain colorless. This fact stands in direct con- 

 trast to what is usually observed, viz., that the pigment- form ing 

 micro-organisms need oxygen for the development of their coloring 

 matter, which therefore appears chiefly or even exclusively at the 

 surface. 



Only one other bacterium, the Bac. lactis erythrogenes, which 

 has been specially studied by Hueppe and Grotenfelt, behaves in 

 this respect like Spirillum rubrum. It may be that Hueppe's view 

 is correct that such bacteria form their pigment as a direct excre- 

 tion as "color ptomaine," quite independent of other influences and 

 conditions. 



On oblique agar and blood- serum the Spirillum rubrum produces 

 a coating with well-defined edges and a moist, transparent appear- 

 ance, which does not spread far from the inoculation scratch. It is 

 at first whitish-gray and afterward rose-red in thickish layers. 



The potato, too, forms a suitable medium, yet here the growth 

 is tardy, and the deep red colonies do not become larger than a 

 hemp-seed. 



While the spirilla generally form only short, incomplete screws 

 on all the solid media, in fluid nutritive solutions, specially in beef- 

 bouillon and sterilized milk, we often find those long-drawn spirals 

 with many coils which have already been mentioned. 



The Sp. rubrum seems to possess no pathogenic qualities. 



SPIRILLUM CONCENTRICUM. 



The Spirillum concentricum is found in putrefying ox-blood, and 

 is perhaps identical with the thick screw-like bacteria which are 

 usually met with in the same. 



Morphologically it behaves in just the same way as Sp. rubrum : 

 it forms short, imperfect screws on solid media, while in fluid ones 

 it produces long screws with many turns- with brisk spontaneous 

 movement and provided with flagella. Like rubrum, too, it is in- 

 clined to degenerate into involution forms, and is without anything 

 that can be clearly proved to be a spore. 



Its growth takes place within tolerably wide limits as to tem- 

 perature, yet it thrives better at ordinary room-temperature than 

 in the incubator. 



