464 THE SPIROCHETES 



contraction of the cylindrical body, relaxing between contractions. In a fluid medi- 

 um the only possible outcome of such contractions is constant rotation of the organ- 

 ism, the spiral membrane propelling the body backward or forward according to the 

 direction of rotation. 



From the mechanical and morphological viewpoint the crista is a giant compound 

 flagellum in which innumerable fibrils are united. It is a homologue of the bacterial 

 flagellum but is unique in structure and disposition. 



Treponema. — In a fluid medium the movement of these organisms is rotatory; 

 in a semisolid medium it is corkscrew-like. Culture forms, when viewed by the dark- 

 field microscope, usually show at one or both ends a fine, rigid filament with numerous 

 regularly set deep spirals. These tiny filaments may be so loosely attached that 

 they swing about as the protoplasm of the terminal section of the organism contracts, 

 but they have no influence upon the movements of the body; their presence is im- 

 material. 



The filaments may occasionally be smooth instead of wavy (Fig. 46), but they 

 are never motile. The terminal filaments undoubtedly represent portions of the axial 

 filament of the mother-cell, which becomes plastic at the time of division and very 

 finely drawn out (Figs. 23, 43). When it divides, each daughter-cell carries away a 

 portion of the maternal axial filament, which subsequently becomes rigid, the material 

 having a tendency to curl when hard. The smooth terminal filaments are probably 

 the drawn-out ends of the periplast, though it may be that the projecting portions 

 of the axial filament occasionally do not become rigid and therefore do not coil. In 

 Figures 43-47 are shown the appearance of the terminal filaments. 



The existence of the axial filament within the body cannot be demonstrated by 

 staining, because it is completely enveloped by a layer of protoplasm which stains 

 far more intensely. Its presence becomes evident, however, during the process of 

 degeneration, whether the latter occurs in the natural course of cultural existence or 

 is brought about by the action of bile or bile salts. The dissolution of the periplast 

 allows the escape of the protoplasm (Fig. 24), and there is left behind the slender 

 hyaline elastic filament with tapering ends and with deep-set and regular windings 

 throughout its length (cf. Figs. 48 and 49, showing appearance before and after treat- 

 ment with bile). The number of spirals of the exposed filament conforms with that 

 of the resting organism. The relaxed organism takes the shape of its axial filament; 

 it is only vigorously motile organisms in which the body is straightened out in places 

 or shows irregularity of the spirals, the result of contraction of the protoplasmic coat. 

 Stained preparations of organisms fixed while actively motile show the same irregular- 

 ities which are observed in fresh preparations. Specimens of treponemas kept some 

 days in the refrigerator are non-motile and show beautiful regular spirals, the larger 

 the species the heavier the axial filament and the greater the distance between the 

 spirals. 



The existence of a delicate periplast is shown by the effect of hypotonicity. In 

 specimens of T. recurrentis, for example, suspended in distilled water, the protoplasm 

 is unevenly distributed, being aggregated at some points into masses which exhibit 

 rhythmic contractions, and absent altogether in other parts, leaving only the axial 

 filament covered by the veil-like periplast (Fig. 25). The periplast finally ruptures. 



