9 8 



MORPHOLOGY AND CULTURE OF MICROORGANISMS 



a large bacillus (2^ wide) almost as large as B. butschlii, and named it, 

 B. flexilis. This species shows exactly the same cytological charac- 

 teristics as B. butschlii (Fig. 76). 



Through a study of a number of different bacteria found in the in- 

 testine of toads, frogs and lizards, Dobell has endeavored to show that 

 this diffuse nucleus is not original, but derived from the retrogression 

 of a more highly differentiated nucleus. 



Thus in various micrococci he was able to show in each cell the 

 existence of a central stainable granule, dividing by constriction at the 

 time of cellular division, and which he regards as a nucleus (Fig. 77, 



12 



FIG. 77. 



FIG. 76. Bacillus flexilis. i, Beginning of the division of a cell about to sporu- 

 late (vestige of sexuality). 2, Disappearance of the incipient division. 3, Forma- 

 tion of the chromatic axial filament. 4, Formation of the beginning of two spores. 

 5, Ripe spores. (After Dobell.) 



FIG. 77. Various bacteria, showing the successive types of the retrogression 

 of the original nucleus and its transformation to a diffuse nucleus. (After Dobell.) 



1-5). In other cocco-bacillary species of bacteria characterized by 

 spherical shape capable of elongation, Dobell discovers a similar nucleus 

 in the spherical cells. When the cell lengthens and assumes the ap- 

 pearance of a bacillus, this nucleus changes to a spiral axial filament 

 (Fig. 77, 5 and 6). 



In various bacilli the same author demonstrates a filament which is 

 ever present (Fig. 77, 7-11). The spore results from the condensation, 

 at one of the poles, in the shape of a large chromatic granule, of part 

 of the grains which compose this filament (Fig. 77, 12 and 13). An 

 interesting variation of this structure is found in B. saccobrinchi. 



