42 THE BACTERIAL CELL. 



0.75-1.0 per cent. These limits are, however, not unconditionally 

 applicable, as the following example will show. A one per cent, 

 solution of common salt produced no plasmolysis in Clostridium 

 butyricum when the cultures were only two days old, and the 

 cells consequently young ; whereas after a further four days they 

 were, without exception, completely plasmolysed. It will perhaps 

 be useful to recall that a solution of 0.5 gram of NaCl in 100 

 grams of water is usually known as physiological salt solution, 

 and is frequently used under the supposition that it neither takes 

 up nor gives up water from or to the cells, an assumption that, 

 in view of the preceding figures, cannot be universally justifiable. 

 If it is desired to render permanent ("fix") the plasmolytic 

 condition of the cells, they must be killed, a result easily obtained 

 by the use of sublimate or iodine solution. Ten per cent, lactic 

 acid is also an excellent fixing medium, instantaneous in action. 

 After fixing, staining can be effected. More detailed informa- 

 tion on the practice of fixing will be found in a work by 



A. ZlMMERMANN (I.). 



35. Structure of the Cell Contents. 



This study, which presents no small difficulty on account of 

 the minuteness of the organisms to be examined, has been closely 

 followed up during the past seven years only. All that was 

 previously known was that the cell contents of the bacteria con- 

 sisted of a homogeneous invacuolate plasma, in which small, highly 

 lustrous granules were frequently seen embedded. 



BUTSCHLI (I.) in 1889 discovered in a few large chromogenic 

 bacteria (e.g. Ghromat'mm Okenii and Opliidomonas jenensis\ as 

 also in Spiroehcete serpens and Beggiatoa, that their cell contents 

 could, as a rule, be distinguishable into two parts, viz., a central 

 body and a parietal layer, the latter being adjacent to and sur- 

 rounded by the cell wall. 



The parietal layer may either surround the central body on all 

 sides, so that the latter nowhere touches the cell wall, or may be 

 restricted to one side only, in which event it is generally, in the 

 case of rod-shaped bacteria, found at the two poles. This differen- 

 tiation of the cell contents can be rendered visible (Fig. 9) by 

 suitable stains, e.g. hsematoxylin, which is most readily taken up 

 by the central body, thereby rendering it easily distinguishable 

 from the more slightly coloured parietal layer. 



This treatment brings out a second and much more important 

 fact : the central body appears as a complicated structure, re- 

 minding one of that seen in honeycomb. A number of granules 

 of red- violet colour called by Biitschli "red grains" are stored 

 in a reticular framework which is coloured blue by the stain- 

 ing dye. These granules do not occur in every cell, and no 

 cell has more than one. These enclosures are detectable, even 



