54 MORPHOLOGY AND CULTURE OF MICROORGANISMS. 



a boat. They are very narrow threads, no one knows how narrow 

 since they cannot be seen without staining and they can only be 

 stained by precipitating some chemical which may add considerably 

 to their width. They are frequently longer than the organism which 

 possesses them and sometimes many times that length. B. sympto- 

 mtici anthracis found in the soil has a flagellum sixty times its 

 own length. The arrangement q the flagella on the bacteria is quite 

 constant 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. 33 and 34). When they are 

 arranged in brushes, the arrangement is spoken of as lophotrichous 

 (Figs. 35 and 36) -and when they are arranged on the entire periphery, the 

 arrangement is said to be peritrichous (Fig. 37). 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 con- 

 nection 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. 



THE HIGHER BACTERIA. 



The higher or trichobacteria are filamentous forms. The filaments 

 sometimes show true branching and frequently false branching. The cells 

 are similar in form throughout the filament and are capable of independent 

 existence, but when growing in the filament give evidence of differentia- 

 tion. Sometimes these filaments are attached to the substratum; in other 

 cases they are free. In the case of the sessile forms, the cells at the attached 

 end are smaller than those at the free end. In other forms the ends 

 may become swollen or club-shaped. Frequently there is a difference 

 between the cells of the different parts of the filaments indicated by the 

 manner of reproduction. Certain cells are apparently set apart for the 

 purpose of reproduction, and, by a process of division, form spores, or 

 gonidia. Some of the free forms of . the trichobacteria move by undula- 

 tive movements of the protoplasm. The exact nature of this movement 



