CLASSIFICATION OF BACTERIA. 23 



The cocci as a rule have no flagella and are consequently 

 stationary. 1 A few forms have been found which possess 

 flagella, and in recent classifications there have been intro- 

 duced the terms Planococcus a,ndPlanosarcina to include the 

 coccus and sarcina forms provided with flagella. These 

 terms have been as yet very little used. 



2. Rod-Shaped Bacteria. Bacillus and Bacterium. In 

 this group are classed all bacteria which are cylindrical in 

 form, either long or short, and either straight or variously 

 bent, though never spiral. Occasionally they are hardly 

 longer than they are broad, while in other cases they form 

 long threads (Fig. 4, b). According to the most recent 

 method of classification they are divided into two groups 

 according to the presence or absence of flagella. 



Bacillus. Rod-shaped bacteria possessing flagella (Fig. 



5). 



Bacterium. Rod-shaped bacteria without flagella (Fig. 

 4, b). It must be noted that this method of separating the 

 two genera, Bacillus and Bacterium, according to the pres- 

 ence of flagella, is a very recent one. Although these two 

 terms have been used in all works on bacteria they have not 

 had the significance above given in any except the most 

 recent publications. In all books on bacteriology published 

 before the last few years the term Bacillus was applied to 

 almost any rod-shaped bacterium, while the term Bacterium 

 had a very uncertain meaning, commonly referring to short 

 rods without spores. The names of many of the best kno.wn 

 bacteria which are in use do not agree with the classifica- 

 tion above given. For example the organism which pro* 

 duces tuberculosis is called a Bacillus (Bacillus tuberculo- 

 sis), although it has no flagella and, according to the classi- 

 fication given, should be a Bacterium. It is not likely that 

 the name will ever be changed. The distinction of Bacillus 



1 Recent work has seemed to show that all cocci have flagella, 

 which are very difficult to demonstrate. 



