8 THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



C; DIFFERENTIATION TECHNIQUES 



(2, 10, 13, 20, 48, 66) 



The mcthylcnc-bluc-cosin method has been used to demonstrate the 

 nuclear material of bacteria which will not stain readily by acid-Gicmsa, it 

 is unfortunately irregular in its results and may be liable to produce artefacts. 



Basically the method is exceedingly simple. The preparation is stained 

 with aqueous methylene blue and diftcrentiated with eosin. The cytoplasm 

 stains pale blue, and the nuclear structures dark blue or purple. In practice, 

 however, it is a diliicult technique to perform, and is not suitable for all strains 

 of bacteria. 



The fdm should be made thick and stained until dark blue throughout. 

 It is then washed in water, differentiated for a few seconds in cosin and 

 immediately washed again. The action of the eosin is very rapid, and it 

 will entirely remove the blue colour if it is allowed to act tor too long. 



It was noted previously that this technique may usefully be employed 

 upon bacteria which resist staining by acid-Giemsa, and the converse is also 

 true. For this reason, methylene-blue-eosin is best regarded as a useful adjunct 

 to acid-Giemsa, and is not recommended as a routine cytological method. 



Similar results arc obtainable by the use of crystal violet, with nigrosin as 

 a differentiating agent. 



D: THE ROMANOWSKY STAINS 



(3^ 47) 



The methylene-blue-eosin technique differs from the better-known staining 

 methods of the Romanowsky type in that the combination of the acidic and 

 basic dyes is permitted to take place during the period of the stainmg reaction. 

 The more orthodox methods arc often of considerable value, however, and 

 simple staining with Giemsa will often prove of value in the case of bacteria, 

 such as myxobacteria and some members of other orders, whose surface 

 structures lack the strong affinity for dyes exhibited by many. Valuable 

 observations have been made in a variety of bacterial groups by the use ot 

 these methods. 



