CLASSIFICATION AND MORPHOLOGY 5 



favourable to the nutrition of the organism causing degeneration, 

 whereby it acquires abnormal aspects, as in old cultures or in media of 

 unsuitable composition. 



Pleomorphism. Recent researches show that the same organism 

 may assume very different aspects, and appear either as bacilli or 

 micrococci. However, pleomorphic organisms are the exception, and 

 it is very unsafe for the beginner to assume, when he finds organisms 

 in his cultures presenting different appearances, that he is dealing 

 with pleomorphic bacteria. 



FLAGELLA OR MOTILE ORGANS. 



All motile bacteria are provided with flagella, which are distin- 

 guished according to their number and position, as follows : 



1. Monotricha, one flagellum at one pole. 



2. Amphitricha, one flagellum at each pole. 



3. Lophotricha, a bundle of flagella at one pole. 



4. Peritricha, many flagella given off around the periphery of the 



organism. 



The above terminology being borrowed from that applied to the 

 Protozoa. 



(For special method of demonstrating Flagella, see 23, 24.) 



THE DIMENSIONS OF BACTERIA. 



These vary as much as their form, and are expressed in microns. 

 A micron is the one- thousandth part of a millimetre, and is desig- 

 nated by the Greek letter /x, i.e.. Bacillus Anthracis, 3-10 /x long, and 

 1-1 '2 fj. broad. Bacillus Tuberculosis, l'5-4 /x long, and only 0*4 /x 

 broad, etc. 



MULTIPLICATION. 



1. Micrococci develop by simple fission (dividing into two trans- 

 versely). 



2. Staphylococci, when forming characteristic grape-like clusters by 

 growth and division in different directions. 



3. Streptococci develop in one direction only, producing chains of 

 varying length. 



4. Sarcince divide regularly in three directions of space, but instead 

 of separating as single cells, remain together in masses like bales of 

 cotton, the individual members, pairs, cubes, etc., being each en- 

 veloped in a capsule. 



