MORPHOLOGY OF THE BACTERIAL CELL 



reproduction. The unbranched filamentous bacteria without definite sheaths 

 are generally classed together under the collective name of Leptothrix. The 

 most complex form is Cladothrix, an aquatic genus with numerous dicho- 

 tomous branchings. Here the cell-chains are enclosed in a separate sheath 

 and the lateral shoots arise by single cells pushing sideways through this 

 envelope and growing out in a new direction. The resulting branch is thus 

 only superficially connected with the parent stem (Figs. 2,/; 12). This 

 is spoken of as ' false branching ' 

 as contrasted with true branching, 

 such as occurs in the mycelium of 

 a fungus (Fig. %,g). In this case 

 one of the cells of the main stem 

 sends out a lateral evagination 

 which, continuing to grow in the 

 new direction, forms a branch. 

 This new member is a lateral out- 

 growth of the parent cell itself, and 

 as intimately connected with the 

 cells of the stem as they are with 

 one another. Among the tricho- 

 bacteria this method of growth is 

 unknown. 



We have now enumerated the 

 various morphological types occur- 

 ring among the bacteria, and there 

 remain to be considered the aggre- 

 gates and colonies which arise 

 among the haplobacteria by the 

 multiplication of the single cell or 

 the proliferation of large numbers 

 in close proximity. The Anthrax 



bacteria, for instance, often form unbranched threads or chains which 

 are externally undistinguishable from those of the true trichobacteria 

 (Fig. 28). Unlike these, however, the anthrax filament may at any time 

 break up into its constituent cells irrespectively'of the advent of the repro- 

 ductive process. Short threads of two or three cells, as well as single cells, 

 may also occur. These phenomena, both in bacilli and cocci, will be con- 

 sidered in more detail when the question of species is under discussion. 

 Very frequently the bacterial cells are found collected in masses of more or 

 less regular contour held together by a gelatinous substance. To these 

 masses the name of Zoogloea has been given. They occur both in liquids 

 and on the surface of solid nutritive substances, such as potatoes or gelatine. 

 Sometimes in liquids they form a skin or pellicle composed of very dense 



B 2 



Fig. 2. a, Spirillum undula, living, with spiral twisting ; 



b, the same dried on the cover glass in semicircular shapes. 



c, Vibrio cholerae, slightly spiral ; d, dried in commaform. e y 

 Spirochaete Obermaieri from the blood in recurrent fever. 

 J, Cladothrix dichotomy a branched example, with sheath 

 and so-called ' false branching ' ; above/' a short branch of 

 two cells is just pushing through the sheath, g, Penicillium 

 g/aucum, a fragment of mycelium with true branching 

 (from Brefeld). Amplification : a and b 1500, c and 4 

 2250, e about 8oo,y6oo, g 120. 



