THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



SECTIONS OF BACTERIA 



Diagrams drawn from electron micrographs of Bacillus cereus are compared. Diagram A 

 is taken from the study by Chapman and HilUer, and B from material prepared in this 

 laboratory. The former has been treated with 2°,, osmium tetroxide which has had the effect 

 of rendering the cell wall very clearly visible but may also have coagulated the softer structures. 

 Section B has been accorded minimal treatment before embedding. The cell envelopes are 

 much less clearly seen, but the arrangement of the various structures is in closer accordance 

 with that seen in stained preparations. 



A — the cell wall has an outer (A) and an inner {A^) layer ; the latter may or may not 

 correspond to the cell membrane. The cross-walls are seen complete (B) and developing by 

 ingrowth {B^) ; an important observation. The material (C) between the inner boundaries 

 of the developing cross-wall, and (C^) at an early stage of their formation, corresponds to the 

 basophilic septum which precedes the true cross-wall. Its present appearance may well be 

 an artefact arising from the coagulation of a much thinner, continuous structure across the 

 cell. Similarly, the extension of the matrix (/->'), in which the nuclei (D) are embedded now 

 extends across the former cell boundaries, at {B^) and (C^). 



B — The cell wall (E) and cross-walls (F) have thickenings (G) at their junctions, such as 

 can be observed by phase-contrast by the method of Tomcsik, and in some stained pre- 

 parations. The cross-walls are indistinct but continuous ; their mode of development cannot 

 be discerned. The matrix (H^) of the nuclear bodies (//) does not extend across the cell 

 boundaries where these have remained complete. 



