THE NATURE OF BACTERIA. 2/ 



twos occasionally called Diplococcus. These terms are going 

 out of use. 



Sarcina. Divisions in three planes, forming solid masses in 

 groups of four or multiples of four (Fig. 6, r). 



The cocci as a rule have no flagella and are consequently 

 stationary. A few forms have been found which possess fla- 

 gella, and in recent classifications there have been introduced 

 the terms Planococcus and Planosarcina 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, U). 

 It must be noted that this method of separating the two genera, 

 Bacillus and Bacterium, according to the presence of flagella, 

 is a very recent one. Although these two terms have been 

 used in all works on bacteria they have not had the signifi- 

 cance 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 veiy uncertain 

 meaning, commonly referring to short rods without spores. 

 The names of many of the best known bacteria which are in 

 use do not agree with the classification above given. For ex- 

 ample the organism which produces tuberculosis is called a 

 Bacillus (Bacillus tuberculosis), although it has no flagella and, 

 according to the classification given, should be a Bacterium. 



