FORM AND STRUCTURE OF BACTERIA 37 



usually necessary to use special stains to" demonstrate capsules 

 clearly. Frequently on stained slides clear spaces are seen 

 around the bacterial cell, and these spaces are often confused 

 with capsules. The spaces are artifacts due to the contraction 

 of the gelatinous capsule during the process of drying. Migula 

 says that in all probability all bacteria possess capsules in a 

 rudimentary state. 



Sheaths. Among certain forms of the trichobacteria 

 (Cladothrix, Crenothrix, etc.) there is developed a structure 

 which has a very similar origin to that of a capsule. The 

 outer layers of the cell wall, instead of remaining soft and ge- 

 latinous, become hard and form what is called a sheath. Phos- 

 phate of lime is deposited in the sheaths of some species of 

 bacteria. The sheaths of bacterial cells in a chain of filament 

 frequently become connected together, making the thread of 

 cells very rigid. The cell proper contracts away from the 

 sheath and is free to move. When reproduction takes place 

 the sheaths break open and the individual cells escape. Sub- 

 sequently the sheath disintegrates (see Fig. 15). 



Mass Grouping. (a) Zooglcea, (6) Pellicles, and (c) Colo- 

 nies. Not infrequently bacterial cells are found collected 

 together in aggregate masses. These masses may have no 

 definite shape, and the individual bacteria are held together by 

 a gelatinous secretion. The individual bacteria may be formed 

 into definite chains. The gelatinous material is either secreted 

 by the cell wall or the outer layers of the cell protoplasm. In 

 all probability it originates from the former. The increased 



