38 PATHOGENIC BACTERIA. 



in chains or solitary and are surrounded by an encase- 

 ment almost cartilaginous in consistence, has been called 

 leuconostoc. 



Certain bacteria, constituting a better-known if not 

 more important group, are not spherical, but elongate 

 or "rod-shaped," and bear the name bacillus (Fig. 3). 



FIG. 3. Diagram illustrating the morphology of the bacilli : a, b, c, various 

 forms of bacilli ; d, e, bacilli with flagella ; f, chain of bacilli, individuals dis- 

 tinct ; g, chain of bacilli, individuals not separated. 



I would remark that the absence of a standard by 

 which to separate the cocci from the bacilli is the cause 

 of much confusion. In the judgment of the author, it 

 would be well to place all individuals having one diam- 

 eter greater than the other among the bacilli. This 

 would prevent the error of describing one species as 

 "oval cocci" and another as "nearly round bacilli," 

 and by giving a definite standard would greatly aid in 

 the formation of a differential table. 



The bacilli present a considerable variety of forms. 

 Some are quite short, with rounded ends, so as to ap- 

 pear elliptical ; some are long and delicate. Some have 

 rounded ends, as subtilis ; others have square ends, as 

 anthrax. Some are enormously large, some exceedingly 

 small. Some are always isolated, never forming threads 

 or chains ; others nearly always occur in these forms. 



The bacilli always divide by transverse fission, so that 

 the only peculiarity of arrangement is the formation of 

 threads or chains. 



In the older writings the short, stout bacilli were all 

 described under the generic term bacterium. This genus, 

 like some of the species it comprehended, has now passed 



