32 THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



Gram-negative cell walls alone show birefringence, and they cannot so readily 

 be freed from the cell membrane by plasmolysis. 



Cytological studies of the cell wall, especially those by Robinow, 

 Klieneberger-Nobel, Bisset and Morris, have owed much to the technique 

 of Eisenberg (1910), perfected by Robinow (1945) of mordanting with tannic 

 acid, which renders it possible to stain the otherwise resistant cell wall with 

 basic dyes, and at the same time destroys the stainability of the cell proteins 

 which enclose and mask the cross-walls and other internal structures. 

 Probably, in addition, the cytoplasmic proteins are precipitated to some extent 

 on the interior of the cell wall, which assists in rendering the outline of the 

 walls stainablc by basic dyes. An even better staining method (Hale, 1953), 

 employing phosphomolybdic acid as a mordant, probably acts in the same 

 way, since these agents are alike in being protein precipitants. The fact that 

 the mature cross-walls resist their action, whereas the basophilic septa are 

 destroyed, constitutes soinc degree of confirmation for the hypothesis that 

 the latter consist of protein whereas the former contain a large polysaccharide 

 component. 



The cross-walls can be seen very easily in bacteria which have been crushed 

 or disrupted and partially emptied of their cell contents. By electron micro- 

 scopy it is only in such material, or in sections, that the septate structure of 

 bacteria can be discerned. However, the desiccation of material prepared for 

 this method of examination may cause the cellular structure of such markedly 

 septate organisms as Mycohacterintn to manifest itself in the form of a row of 

 granules, rather like their beaded appearance in Zichl-Ncelscn stained pre- 

 parations. In electron microscope studies by workers apparently unaware 

 of the septate structure of Mycohacterinw, these granules have been identified 

 with a variety of intracellular structures, for example, nuclei, sap-vacuolcs, 

 and mitochondria. 



It is not suggested that none of the structures described form part of these 

 granular aggregates, indeed the nuclei must necessarily do so ; but the 

 identification of a structure which comprises so high a proportion of any one 

 of the relatively tiny component cells of these multicellular bacteria with any 

 single cytoplasmic component, on the evidence of a fancied resemblance in 

 an electron micrograph, is exceedingly difficult to justify. 



