GENERAL CHARACTERS OF SPIROCTLETES. 13 



and-fro like the lash of a whip, the spirilla confine them- 

 selves almost entirely to a rapid "cork-screw" motion, 

 with little alteration in the long axis of the body. A 

 certain degree of the latter motion may, however, at 

 times be observed in them, so that this difference is 

 rather quantitative than one of kind. 



Failure to cultivate spirochaetes, large or small, in 

 artificial media has been urged as a reason for regard- 

 ing them as protozoa and not bacteria, but this argu- 

 ment again is of little weight, since, not all known 

 bacteria can be grown artificially (e.g., B. leprcs), and 

 the quality of adaptability to cultivation in the labora- 

 tory can hardly be looked upon as essential to this or 

 any other class. Indeed, some of the protozoa can be 

 cultivated; for example, some forms of amoebae and of 

 flagellata. 



The curious arrangement of the staining material 

 in the body of the larger spirochaetes, which has been 

 regarded as constituting a special nucleus, has been held 

 to prove their animal nature ; but there is at present too 

 much uncertainty as to the constitution of this staining 

 substance and its formation in these organisms to allow 

 of any great weight being assigned to this peculiarity 

 for purposes of classification. Schwellengrebel states 

 that a spiral filament similar to that found in Sp. bal- 

 bianii may be found in Spirillum giganteum, though his 

 statement has not so far been confirmed. Certainly a 

 resemblance exists between the form taken by the 

 staining substance in this spirillum and that seen in 

 some spirochaetes (Figs. 8,9,10). 



Other peculiarities of the large spirochaetes which are 

 regarded as protozoan characteristics are the asserted 

 existence of an undulating membrane, the lack of 

 flagella, and the habit of longitudinal division for pur- 

 poses of multiplication. With regard to the first of 



