196 TEXT-BOOK OF BACTERIOLOGY. 



On the gelatin plate grayish- white, round colonies of middle 

 size develop rather quickly. These are seen under the microscope 

 as sharp- edged, slight! y- granulated discs. If they reach the sur- 

 face of the food medium, they often show a peculiar concentric 

 arrangement, narrow transparent rings, alternating with broad 

 opaque ones, so that the whole bears some resemblance to a 

 cockade. 



The gelatin is not liquefied. 



In stab- culture the growth takes place more at the surface than 

 in the depths. It is striking that the neighborhood of the puncture 

 is gradually occupied more and more by the culture. The spirilla 

 bore into the solid gelatin, and push forward through it; this be- 

 havior is particularly noticeable in scratch cultures on oblique 

 gelatin. From a tough bacterial growth on the surface a cloudy- 

 looking whitish-gray substance extends down to the very bottom. 



The development on agar offers nothing remarkable; on pota- 

 toes no growth takes place. 



As far as we know, the Spirillum concentricum is as destitute of 

 pathogenic qualities as the Sp. rubrum. 



This is all that will be said of the non- pathogenic bacteria, al- 

 though the consideration of them has been incomplete in two re- 

 spects. 



On the one hand, there are many bacteria which have been ex- 

 amined by the new methods of research and found to be well-de- 

 fined and separate species, but which have not been described 

 because they do not possess for us sufficient importance to merit 

 special attention. 



On the other hand, there are other bacteria which occupy an 

 important and prominent place in books on bacteriology, especially 

 older ones, and might therefore seem to deserve notice. But all of 

 them Micrococcus ureas, Bacterium aceti, Bacillus ulna, Ascococ- 

 cus Billrothii, etc. share the fate of Bacterium termo. They are so 

 many denominations which will remain without value for us until 

 the modern means of investigation shall have yielded more infor- 

 mation about them and enabled us to say precisely what we under- 

 stand by them. 



Until that has been done such names have only a historical im- 

 portance, and the writer must be excused if they are passed over in 

 silence. 



