96 



MORPHOLOGY AND CULTURE OF MICROORGANISMS 



The latter investigator.discovered, in the intestines of frogs and toads, 

 a large bacillus (a^u wide) almost as large as B. biltschlii, and named it, 

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

 teristics as B. biifschlii (Fig. 74). 



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. 75, 



Fig. 74. Fig. 75. 



Fig. 74. — Bacillus flexilis. i, Beginning of the division of a cell about to sporu- 

 late (vestige of sexuaUty). 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. 75. — 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. .75, sand 6). 



In various bacilli the same author demonstrates a filament which is 

 ever prpsent (!Fig. 75, 7-1 1). The spore results from the condensation, 

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



