34 Structure and Classification of Micro-organisms 



2. Crenothrix. Cells united to form unbranched threads which 



in the beginning divide transversely. Later the cells 

 divide in all three directions of space. The products of 

 final division become spheric, and serve as reproductive 

 elements. 



3. Phragmidiothrix. Cells at first united into unbranched 



threads. Divide in three directions of space. Late in the 

 development, by the growth of certain of the cells through 

 the delicate, closely approximated sheath, branched forms 

 are produced. 



4. Thiothrix. Unbranched cells inclosed in a delicate sheath. 



Non-motile. Division in one direction of space. Cells 

 contain sulphur grains. 



II. ORDER: THIOBACTERIA (Sulphur Bacteria). 



I. Family BEGGIATOACE.. Cells united to form threads which are 

 not surrounded by an inclosing sheath. The septa are scarcely 

 visible. Divide in one direction of space only. Motility ac- 

 complished through the presence of an undulating membrane. 

 Cells contain sulphur grains. 



There are two families, numerous subfamilies, and thirteen genera in 

 this order. They are all micro-organisms of the water and soil, and 

 have no interest for the medical student. 



Structure. Nucleus. When subjected to the action of 

 nuclear stains, large vague nuclear formations are usually 

 observed in the bacterial cells. 



Cytoplasm. The cytoplasm, of which very little exists 

 between the large nucleus and cell- wall, is sometimes granu- 

 lar, as in Bacillus megatherium, and sometimes contains fine 

 granules of chlorophyl, sulphur, fat, or pigment. 



Capsule. Each cell is surrounded by a distinct cell- wall, 

 which in some species shows the cellulose reaction with 

 iodin. 



The cell-walls of certain bacteria at times undergo a 

 peculiar gelatinous change or permit the exudation of 

 gelatinous material from the cytoplasm, and appear sur- 

 rounded by a halo or capsule. Such capsules are seen about 

 the pneumococcus as found in blood or sputum, Friedlander's 

 bacillus, as seen in sputum, Bacillus aero genes capsulatus in 

 blood or tissue, and many other organisms. Friedlander 

 pointed out that the capsule of his pneumonia bacillus, as 

 found in the lung tissue or in the "prune-juice" sputum, 

 was very distinct, though it could not be demonstrated at 

 all when the organisms grew in gelatin. 



Polar Granules. By carefully staining an appropriate 

 organism certain peculiarities of structure can sometimes 

 be shown. Thus, some bacilli contain distinct " polar gran- 

 ules" (metachromatic or Babes-Ernst granules) rounded or 



