XII.] BACTERIA. 413 



6. Besides the form hitherto described, which would 

 be known as Arthrobacterium, many other Schi- 

 zomycetes will certainly be found, both in the 

 pellicle and the fluid beneath. The following may 

 be especially mentioned : 



a. Micrococcus. Bodies much like Arthrobacterium 

 but short and rounded, and occurring singly, or 

 in bead-like rows. They may be found free or 

 in a Zoogloea stage. 



b. Bacillus. Threads composed of straight cylin- 

 drical joints much longer than those of Arthro- 

 bacterium, but of similar structure: they are al- 

 ways free-swimming. 



c. Vibrio. Like Bacillus, but with bent joints. 



d. Spirillum. Elongated unjointed threads rolled 

 up into a more or less perfect spiral : frequently 

 two spirals interwine. In some of the largest 

 forms a vibratile cilium can be made out on 

 each end of the thread. 



e. Spirochaete. Much like Spirillum, but longer 

 and with a much more closely rolled spiral. A 

 very actively motile but not common form. 



7. Examine various putrefying substances for different 

 forms of Bacteria. Successful cultures may be 

 made on hard-boiled white of egg, or slices of 

 potato, kept moist under a bell-glass. Various 

 brilliantly coloured micrococci including the blood- 

 red " Micrococcus prodigiosus " will make their 

 appearance on such cultures. An infusion of pea- 

 flour, filtered, is especially favourable for Spiro- 

 chsete. 



