TEXT-BOOK OF BACTERIOLOGY. 161 



slowly, when slight obstacles to growth prevent a too speedy dis- 

 integration of the individual cells into new-formed elements. Thus 

 in slightly acid food media which are not quite favorable to the 

 development of the prodigiosus, Wasserzug and Ktibler saw such 

 strings, or chains, arise very frequently — a fact which, of course, 

 removes the last doubt as to the fact that this micro-organism is a 

 bacillus, and not a micrococcus. 



The Micrococcus prodigiosus, in consequence of the facts just 

 mentioned, has been robbed of the name it had so long borne and 

 under which it had become known to science, and has been described 

 as " bacillus " prodigiosus. It possesses the faculty of spontaneous 

 movement. It is true that generally its movement is but little 

 noticeable. It is best seen under the unfavorable conditions of 

 growth just mentioned — for example, in certain substrata or in 

 strongly-diluted fluid media. Schottelius explains this fact by say- 

 ing that, as a rule, the cells are surrounded by a close, glassy 

 mucus, which hinders locomotion and cements the individual organ- 

 isms to each other. Only when the formation of this membrane is 

 checked is spontaneous motion visible. 



The existence of spores has not yet been observed. Neverthe- 

 less it is a remarkable fact that the prodigiosus retains its vitality 

 for a long time in a dry state. A certain amount of moisture is 

 doubtless necessary for its growth ; yet if we transfer small por- 

 tions of a potato culture to a silk thread, or lay them between 

 sheets of blotting-paper, we can from this seed provoke a rich 

 growth on a fresh >food medium, even after several months. 



The Micrococcus prodigiosus does not thrive as well in the in- 

 cubator as. at ordinary room-temperature. It is so little sensitive 

 to a want of oxygen that it may be reckoned among the semi- 

 anaerobic species. 



Differences in the formation and composition of the cells are not, 

 as a rule, visible; yet occasionally, when the cover-glass prepara- 

 tions are treated with anilin stains, one may notice in the middle 

 of the cells small shining gaps, which at the first glance might be 

 taken for spores. They are, however, connected with the process 

 of segmentation, and show the spot where fission is commencing. 



On the gelatin plate the colonies of the M, prodigiosus have a 

 different appearance, according as they lie in the interior of the 

 mass or reach the surface of it. The former appear to the naked 

 eye as small white points, while the microscope shows them as 

 greenish-brown roundish masses, irregularly fringed at their edges. 

 The surface colonies show the two chief peculiarities which the 

 prodigiosus develops when it is in contact with the oxygen of the 



