24 MORPHOLOGY OF BACTERIA. 



shape. Some are quite short and thick ; others long and 

 slender ; some very large and some very small. They may 

 be so short as to resemble a coccus, hence the term oval 

 coccus. Some have rounded ends ; others pointed, squared, 

 or slightly concave ends. They may be spindle-shaped, rod- 

 shaped, club-shaped, or a clostridium shape. Their arrange- 

 ment is in some instances characteristic. They may be seen 

 to lie singly or in pairs, in parallel rows or in chains of vary- 

 ing length, sometimes interlacing freely. Very long, slender, 

 and indistinctly articulated filamentous bacilli are known as 

 leptothrix; when these filaments present pseudobranchings, 

 they are termed cladothrix. 



The spirilla (Fig. 7) are curved or twisted rods of varying 

 length, endowed with motility and a peculiar rotary move- 

 ment, flagellated and reproducing themselves by both fission 



FIG. 7. 



a 6 c d 



a and d. Spirilla in short segments and longer threads the so-called comma 

 forms and spirals. 6. The forms known as spirochseta. c. The thick spirals some- 

 times known as vibrios. (Abbott.) 



and sporulation. They may be very rigid or exceedingly 

 flexible. The short, slightly bent rods resemble a comma so 

 closely that they frequently are referred to as " comma " bacilli 

 (cholera), or as a vibrio because of their vibratory motion. 

 The extremely long and flexible forms are called spirochceta 

 (relapsing fever). A spiromonas is a ribbon-shaped spirillum. 

 When sulphur granules are found in the protoplasm of the 

 organism, it is called an ophidomonas. 



Several higher forms of bacteria also are recognized. They 

 approach the plant in structure and method of growth. 

 Among these is the streptothrix, the only form which is en- 

 countered in animal pathology. The Streptothrix actinomyces 

 (ray fungus) (Fig. 8) is the type of this class. The tubercle 



