106 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



and is used by some authors to differentiate genera. Very few of the 

 micrococci are provided with flagella, as was indicated above, and in 

 the bacilli and spirilla they may be arranged at the poles singly or in 

 brushes, or they may be arranged on the entire periphery of the cells. 

 When bacteria are provided with a single flagellum at one pole, the 

 arrangement is said to be monotrichous (Figs. 82, 83 and 84). When they 

 are arranged in brushes, the arrangement is spoken of as lophotrichous 

 (Figs. 85 and 86) and when they are arranged on the entire periphery, 

 the arrangement is said to be peritrichous (Fig. 87). It frequently 

 happens that in the case of the monotrichous and lophotrichous the 

 flagella occur at both ends of the organism. This is explained by the 

 fact that the organism is just undergoing binary fission and that the 

 second group is on the newly forming cell. It is worth while in this 

 connection to call attention to the fact that the flagella on one end are 

 new, while those on the other end may be thousands of generations old. 



Minute Consideration of Flagella.* The question of the cilia or 

 flagella of bacteria is not yet entirely decided. The absence of cilia 

 in large bacteria capable of motion gives the idea that these are not the 

 only organs of motion, and that contraction of the protoplasm certainly 

 plays the most important role in the phenomena of motility. More- 

 over, the nature of cilia has been debated. Van Tieghem and Biitschli, 

 taking their stand primarily on the difficulty of staining cilia by the 

 reagents which rapidly color protoplasm, have considered these cilia 

 to be simply prolongations of the membrane, lacking all contractibility 

 and locomotive power. According to Van Tieghem, when two cells 

 formed by the division of the same element separate, the common por- 

 tion of the transverse septum, instead of dividing neatly in two, can 

 stretch out into a filament which breaks at a greater or less distance from 

 each of the two daughter cells. This prolongation composes the 

 vibratile cilium. 



This theory, however, does not explain the existence in certain 

 bacteria of clusters of cilia at the two poles, or of cilia distributed over 

 the whole surface of the membrane. Other authors, as for example 

 A. Fischer, consider the cilia true prolongations of the protoplasm 

 issuing through tiny apertures in the membrane. This view at present 

 tends more and more to predominate, and the existence of flagella on 

 bacteria appears to be demonstrated. 



Prepared by A. Guilliermond. 



