HIDEYO NOGUCHI 463 



that these appendages are similar in structure to bacterial flagella, nor does their 

 presence explain the characteristic spirochetal movements. 



The tendency in the past has been to attack the problem of the structure of 

 spirochetes by cytological methods, i.e., by the study of individuals fixed and stained 

 in such a way as to preserve the normal structure as nearly as possible. Such methods 

 are less productive in the case of spirochetes than a study of involution or degenera- 

 tion phenomena. Destruction of the less resistant elements of the body by induced 

 degeneration, e.g., by exposure of the organisms to the action of certain cytolytic 

 agents, bile, or bile salts, gives a clue to the type of skeletal structure present. Changes 

 in the tonicity of the medium serve to indicate whether a periplast is present and of 

 what nature it is. Observation of the morphological sequences in division and the 

 natural process of degeneration also furnish information regarding structure and 

 motility. 



From a study of the degeneration phenomena of several types of spirochetes the 

 writer has concluded that the kinetic element in these organisms is the axial filament, 

 which is a kind of modified flagellum. The reasons for this deduction will appear in 

 the separate discussions of the various genera given below, 



Cristispira. — This very large, wormlike organism was once known as a trypano- 

 some because of its veil-like membrane. It is found in a rather firm, gelatinous, hya- 

 line structure of shellfish known as the "crystalline style," which is situated in the 

 esophagus. The style, which dissolves rather readily in sea water after extraction 

 from the oyster or clam, often contains a large number of the large, very active spiro- 

 chetes, swimming by means of a membranous structure, one edge of which is free, 

 the other attached longitudinally along a line which winds about the body spirally 

 (Figs. 19-21, 40-42), This structure was shown by Gross to be different from the 

 undulating membrane of a trypanosome and was designated by him the "crista," 

 The body itself is not spiral. The periplast is heavy, and the protoplasm is divided 

 into numerous small chambers by transverse septa (Figs, 40-42), The organism is 

 devoid of an axial or terminal filament. 



The membrane is thicker at the outer edge than where attached to the body and 

 frilled. Little idea of the structure can be gained from direct observation of living 

 forms (Figs, 35-36) or from stained preparations of normal organisms. When the or- 

 ganisms in the style have died, however, and they do not survive long after the style is 

 removed from the shellfish, many detached cristas are found. They retain their spiral 

 shape (Fig, 38), and when they break up into shorter pieces numerous fibrils are 

 plainly recognizable (Fig, 39), These vary in length and thickness but are all wavy, 

 tapered at the ends, hyaline, and firm in appearance. They lie parallel or may be in- 

 terwoven in a sort of mesh. The individual fibrils do not fragment or bend sharply 

 but appear to be elastic, and they retain their staining property even after they sepa- 

 rate from the mass. Those at the free edge are thicker and longer and form a dis- 

 tinct bundle. 



The body form of the resting or dead organism is wavy (Fig, 37), i,e,, it conforms 

 to the shape of the spring-like crista. It is difficult to follow the shapes taken by 

 the body in motion, but it seems to straighten and relax in rapid alternation. It is clear 

 that the elastic wavy membrane is stretched at short intervals by the rhythmical 



