THE SPIROCH^TES 115 



the genus in which to place the blood-inhabiting forms is somewhat 

 uncertain and disputed. Various generic names given to them are 

 Spirochata, Treponema, Spiroschaudinnia (Sambon) and Borrelia 

 (Swellengrebel). Included in this division are the causal agents of 

 relapsing or recurrent fever. These Protists will be named, for 

 description, Spirochaetes without prejudice as to the ultimate correct 

 generic name. 



It is sometimes made a matter of argument as to whether the 

 spirochaetes are Protozoa or Bacteria. Such arguments are somewhat 

 unprofitable. Morphologically the spirochaetes are like the Bacteria 

 in possessing a diffuse nucleus. They differ from Spirillum, an 

 undoubted bacterial genus, in being flexible and not possessing 

 flagella. Molluscan spirochaetes, however, may appear to have 

 flagella if their membrane becomes frayed or ruptured, when the 

 myonemes therein (fig. 53), becoming separated, form apparent 

 threads or flagella (Fantham, 1 907-08). * 



Again, the mode of division of spirochaetes has been used as a 

 criterion of their bacterial or protozoal affinity. They have been 

 slated to divide transversely, longitudinally, and by " incurvation," 

 or bending on themselves in the form of a U, "a form of transverse 

 fission." The present writer believes that they divide both transversely 

 and longitudinally, and that there is a periodicity in their mode of 

 division at first longitudinal (when there are few spirochaetes in, say, 

 the blood) and then transversely (when spirochaetes are numerous in 

 the blood). 2 Some authors consider that longitudinal division is ex- 

 plained by "incurvation." 



The spirochaetes of relapsing fever show a remarkable periodic 

 increase and decrease in numbers in the blood. They are transmitted 

 by ticks or by lice. They react to drugs (e.g., salvarsan or " 606 ") 

 rather like trypanosomes, and like Protozoa, but unlike Bacteria 

 they are cultivated with difficulty. These and other criteria have been 

 used to endeavour to determine whether they are Protozoa or Bacteria. 

 The present writer believes that they are intermediate in character, 

 showing morphological affinities with the Bacteria and physiological 

 and therapeutical affinities with the Protozoa. The group Spiro- 

 chaetacea, as an appendix to the Protozoa, has been created for them 

 by the present writer (Jan., 1908). Others have placed them in the 

 Spirochaetoidea of the Bacteria or with the Spirillacea. Doflein (1909) 

 called them Proflagellata. Further discussion is unnecessary, as they 

 are undoubtedly Protista (see p. 29). 



There is no true conjugation, sex or encystment in spirochaetes, 

 but morphological variation may occur. 3 They may agglomerate. 



1 Quart. Journ. Microsc. Set., Hi, p. I. 2 Proc. Roy. Sac., B, Ixxxi, p. 500. 



3 Fantham, Parasitology, ii, p. 392. 



