THE STRUCTURE OF BACTERIA. 35 



the genus Bacterium or Arthrobacterium, and 

 the tubercle rods are not true bacteria at all, 

 but a parasitic form of the tubercle mould. 



A step further indeed may now be taken. 

 The name Bacillus may be limited to that 

 genus in which the rods undergo no change in 

 shape during spore-formation, and we may use 

 the term Clostridium for that genus in which 

 the rods are spindle-shaped or become spindle- 

 shaped during spore-formation, and designate 

 as Plectridium that in which the cells are 

 shaped like a drumstick or become so shaped 

 through the development of endospores. With 

 reference to spore-formation, therefore, there 

 are among the rod bacteria three genera of 

 endosporous and one of arthrosporous bacteria. 

 These may be still further analyzed into sub- 

 genera if we take into consideration the form 

 of the spores, or, as Fischer has suggested, the 

 character of the flagella. 



Among the spiral bacteria Cohn constituted 

 the form-genera Vibrio, Spirochczte and Spi- 

 rillum merely upon the basis of the form 

 of spiral. I would establish here a division 

 into natural genera, calling those spirals 

 which do not change in shape during endo- 

 spore-formation Spirillum, and applying the 

 name Vibrio to those that become swollen in 

 some one place when endospores are formed, 



