4 PRACTICAL BACTER OLOGY 



from a botanical point of view. The three principal divisions are as 

 follows : 



1. Cocci or Micrococci, or round organisms. 



%. Bacilli, or rod organisms. 



3. Spirilla, or spiral organisms. 



1. The Cocci or Micrococci are subdivided as follows : 



(1.) Staphylococci growing like bunches of grapes. 



(2.) Streptococci growing in chains. 



(3.) Diplococci growing in pairs. 



(4.) Tetrads developing in fours. 



(5.) Sarcinae dividing into fours, eights, etc., as cubes. 



All spherical forms belong to this group, the isolated individual 

 member^ of which are practically of the same diameter in all directions. 



2. The Bacilli include all straight, rod-like bacteria in which one 

 diameter is always greater than the other. Many of the organisms 

 belonging to this group in the course of development deviate from 

 the simple rod shape, and when very short, i.e., multiplying rapidly, 

 appear like micrococci ; the ends of rods also vary in shape according 

 to the particular organism, being either blunt or rounded. 



3. The Spirilla are subdivided as follows : 



(1.) Vibrio, or short spirals. 



(2.) Spirillum, or long rigid spirals. 



(3.) Spirochaete, or long flexible spirals. 



Different bacteria may, moreover, be characterised by the following 

 peculiarities: They may form Zooglcea, by which we understand 

 bacterial aglomerations of bacteria in large numbers enclosed in an 

 amorphous matrix, which may give great tenacity to the bacterial 

 mass. 



By Ascococcus we understand cocci, associated in large numbers in 

 an amorphous matrix, and enclosed in an enveloping membrane. 



Some bacteria possess a distinct capsule, and are known as Capsule 

 cocci and Capsule bacilli, the capsule being more or less evident, 

 depending upon the conditions of growth. 



By Leptothrix we understand long undulating rods. 



By Cladothrix, long, straight and branching rods. 



By Streptothrix, organisms that in their structure resemble at one 

 time the thread fungi, and at other times the bacteria; like the mould 

 fungi, they form cylindrical threads out of round cells, which branch 

 dichotomously, finally becoming visible to the naked eye as irregular 

 radiating thread masses or mycelia. 



Involution Jorms of bacteria usually occur under conditions un- 



