THE SPIROCHETES 149 



On the other hand, members of the genus Spirillum are 

 characterised by the possession of fine protoplasmic processes 

 (cilia or flagella) as outgrowths of the body, and the latter is 

 rather more rigid and so less sinuous than that of a Spirochete. 



Unfortunately the generic and specific characters of these 

 and of related forms are in a most confused state, and in 

 some memoirs by well-known workers mention is made of 

 the " Spirochetes of Spirillosis." 



The general shape of a Spirochete is, as previously men- 

 tioned, that of a long, narrow, wavy thread, which is at once 

 suggestive of a bacterial organism. Some Spirochetes, how- 

 ever, are very large for Bacteria. The body is bounded 

 externally by a definite, but flexible and very thin layer, 

 which has received the name of periplast. 



Fig. I. (a) Spirochete!, plieatilis (Ehrenberg), end portion of a long individual. The 

 central axis (black) is the nucleus, and is surrounded by the endoplasm and the 

 ectoplasmic undulating membrane. In this figure (after Schaudinn) the ectoplasmic 

 and endoplasmic structures are not clearly differentiated from each other. 



(b) Spirochceta refringens, after Schaudinn. 



(c) Treponema pallidum (Spirochata pallida\ after Schaudinn. 



The possession of a specially differentiated portion of pro- 

 toplasm, known as the nucleus, is characteristic of most 

 unicellular organisms, especially animal ones. The chief con- 

 stituent of this nucleus is a substance known as chromatin, 

 on account of its capacity for taking up various stains and 

 being coloured thereby. 



Usually the nucleus is condensed, and so is well marked 

 after staining. Its position in the cell is often central. The 

 principal exception to this is found in the Bacteria, which 



