CLASSIFICATION OF BACTERIA 13 



direction. The cocci are arranged in chains or bead-like 

 formation. 



(3) Tetracoccus, or Merismopedia. — Division in two direc- 

 tions, forming groups of four, which remain associated in a 

 single plane, giving rise to tablet-like layers of cells. 



(4) Sarcina, or Packet-cocci. — Division in three direc- 

 tions, forming packets of eight or more elements, which 

 remain associated in more or less cubical masses. 



Cocci may also occur singly, in groups, and in chains, 

 "surrounded by a gelatinous envelope, which often cause the 

 organisms to agglutinate together in a mass. This form is 

 known as a Zooglaea. 



Bacteriaeeae — (1) Bacillus. — The straight, rod-like bac- 

 teria ; reproduction by binary division, or by resting spores ; 

 are, as a rule, motile. When, owing to spore formation 

 in the end of the rod, it gives rise to peculiar enlargement 

 resembling a bottle, the bacillus is known as a Clostridium. 



(2) Spiro-bacteria, or Spirilla. — These .form curved or 

 spiral filaments, rigid or flexible ; reproduction by binary 

 division and by spore formation ; movements rotatory in 

 the direction of the long axis of the filaments, or they may 

 be motionless. 



Spirilla are subdivided into ' comma ' bacilli or vibrios, 

 spirilla in the more restricted sense, and spirochsetge. The 

 vibrios usually form strings of cells which strongly resemble 

 spirilla ; the spirochsetse are distinguished for their flexi- 

 bility. 



Certain bacilli, as in the case of cocci, also occur singly 

 and in chains which are surrounded by a gelatinous 

 envelope, which often causes the organisms to become 

 agglutinated into masses. This form is known as a 

 Zooglaea. 



Leptotricliese. — These form rodlets and longish threads, 

 which show a distinction between the base and apex of the 



