GENERAL CHARACTERISTICS OF THE SPIROCHETES 909 



(Hindle 1925). They are found in the tissues of patients with Weil's disease and 

 other leptospiral infections. In length they vary from about 6-85 /.i, but are 

 generally about 9-12 /* ; their thickness is only about 0-1 ju. The length of the 

 middle portion is variable, but the hooked ends are always of about the same 

 size, suggesting that growth may occur only in the middle portion (Zuelzer 1925). 

 No internal structure can be distinguished in electron micrographs, nor can flagellum- 

 like bodies, similar to those observed in some of the treponemata, be seen (Morton 

 and Anderson 1943). . 



The brief accoxint that has been given of the different groups is necessarily 

 dogmatic, and it may well be that further work will necessitate a revision of our 

 present classification. 



General Characteristics of the Spirochetes 



Morphology. — With the exception of the structures seen in electron micro- 

 graphs of some of the treponemata (see p. 908), spirochsetes are generally regarded 

 as being without flagella ; they are nevertheless motile. Three kinds of move- 

 ment are generally described : (1) Movements of flexion, in which the whole 

 organism undergoes a change in shape. As a rule the natural shape of a spirochsete 

 at rest is straight ; but during movement all sorts of twists and turns may develop, 

 one form following another in rapid succession, but each one tending to return to 

 the normal straight form. During these movements of flexion the primary spirals 

 remain unaltered. (2) Movements of rotation around the long axis ; these are 

 difficult to see unless the ends of the organism are bent at an angle to the main 

 axis, when the rotatory movement is especially apparent. When the rotation is 

 very rapid, and when as in Leptospira the ends are hooked, the spirochsete may 

 take on the appearance of a spiral thread with a button-hole at each end. (3) 

 Movements of translation, by which the organism changes its position, moving 

 from one place to another. This change in place is probably dependent upon the 

 rotatory movement, which acts like a propeller driving the organism forwards or 

 backwards according to the direction of the rotation. 



Different spirochaetes vary greatly in their activity ; some, for example, exhibit 

 very active movements of flexion, lashing furiously in various directions, but 

 making very little progress from their original position ; others dart rapidly hither 

 and thither, rendering their ocular pursuit almost impossible. 



Multiplication occurs by transverse fission. It is not clear, however, whether 

 the organism always divides in the middle giving rise to two shorter spirochaetes 

 of equal length, or whether division occurs at times asymmetrically. According 

 to Seguin's (1930) observations on Trep. calligyrum and Trep. gallinarum, and 

 Manouelian's (1940) observations on Trep. pallidum, asymmetrical division, at 

 least in cultures, is not uncommon, the shorter cell seen after separation having 

 only two, one, or even less than one complete spiral. Again, whether the large 

 knob- like bodies seen attached to some of the treponemata play any part in repro- 

 duction is still doubtful. 



Generally speaking, the spirochaetes are more difficult to stain than the bacteria. 

 Methylene blue, which is usually a satisfactory bacterial stain, leaves many of the 

 spirochaetes unstained. It has been suggested that the spirochaetes are devoid of 

 nucleo-protein, and to the absence of this substance has been ascribed the failure 

 of the treponemata and all the known leptospirae to stain with this dye. On the 

 other hand, the fact that an organism does stain with methylene blue is no proof 



