CHAPTER II. 



STRUCTURE AND CONSTITUTION OF THE BACTERIAL CELL. 



31. Chemical Composition of the Cell Wall. 



NAKED cells, i.e. those wherein the protoplasma is unprotected by an envelope 

 are unknown amongst schizomycetes, the body of the cell being in all fission 

 fungi shut off from the outer world by a membrane or cell wall. Little is as 

 yet known regarding its chemical composition, but the few investigations that 

 have been made in this direction demonstrate that we have to do with a structure 

 which not only differs in different species, but also undergoes alteration according 

 to the dietary of the cell. 



The proximate assumption that the cell wall of the fission fungi consists of 

 cellulose cannot withstand searching criticism except in rare instances. At 

 present only one single species, viz., the Bacterium xylinum, examined by O. 

 LOEW and A. J. BROWN (I.), for which this assumption is justified, is known. 

 The cell walls of this acetic acid bacterium exhibit, after a suitable purification, 

 the following chemical composition, ascertained by ultimate analysis : 



Calculated 

 Fouud. for [C 6 Hi O 5 ]H. 



Carbon 44.26 44.44 



Hydrogen 6. 25 6. 1 7 



Oxygen 49.49 49-39 



The cell wall of this microbe is stained blue by aqueous or alcoholic solutions 

 of iodine, by iodine and sulphuric acid, and with iodo-chloride of zinc. In a 

 work from the pen of DREYFUSS (I.), dealing, however, chiefly with higher fungi, 

 and therefore preferably to be considered only in the second volume, a tew species 

 of fission fungi were included in the scope of investigation (e.g. a culture of hay 

 bacillus obtained according to Roberts' directions). These when tested for 

 cellulose by iodine yielded affirmative results. The amount was, however, only 

 very small. According to NENCKI and SCHAFFER (I.), the cell wall of certain 

 putrefactive bacteria contains nitrogen ; but they do not give the names of the 

 species. 



32. Optical Properties of the Cell Wall. 



Yet another means has been employed for obtaining an insight into the 

 chemical nature of the cell membrane of the fission fungi, namely, its optical 

 behaviour. 



The cell walls of the higher plants are known to be anisotropic (doubly 

 refractive), a property also employed by F. v. Hohnel as a means of differen- 

 tiating textile fibres. Jf a couple of cotton fibres be placed on the stage of a. 

 polarising microscope, the Nicol prisms of which are crossed, the plane of oscilla- 

 tion of the polarised daylight issuing from the lower Nicol undergoes, in its 

 passage through the doubly refractive threads, a rotation, in consequence of 

 which the fibres appear bright and coloured against the dark background. Jf 

 the fibres are themselves coloured or dyed, they assume the corresponding 

 complementary colours, 



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