STAIXIXfi o| MICROORGANISMS 67 



cesses have been established in the course of the researches 

 which have been made up to the present that we must 

 describe them here more in detail, especially as they afford 

 marks by which bacteria can be distinguished, and 

 consequently staining is of the highest importance in 

 determining the individual varieties. 



Staining of micro-organisms. Staining constitutes an 

 indispensable aid to the study of the finer structure 

 of the micro-organisms, and of their relation to the cells 

 of the body. In carrying it out a series of colouring 

 matters are used which have been already detailed (p. 30), 

 and solutions are prepared from these in different ways, 

 which are employed both for isolated micro-organisms 

 and also for those in the tissues. The basic aniline 

 colours are for the most part kept in stock in alcoholic 

 solutions which are mixed with water before use, so that 

 we really employ a dilute alcoholic solution in staining. 

 The dilution, however, must not be carried too far. 



Giinther has pointed out that absolute alcohol is not 

 suitable for use in staining with basic aniline colours, just 

 as it is incapable of extracting the dye from cells when 

 once they have been stained. 



Simple staining of cover-glass preparations. In this, the 

 simplest kind of staining, the mode of procedure is as 

 follows : A sample of the matter to be examined is con- 

 veyed on to a cover-glass with the point of the sterilised 

 platinum needle and is diluted, if needful, with water, after 

 which the organisms suspended in the water are spread 

 out over the surface of the glass with the flattened end of 

 the needle (smear preparation) ; or a better way of managing 

 this is to press another cover-glass upon the prepared one, 

 and then slide it off, so that the mass -under examination 

 appears equally distributed on both cover-glasses. The 

 mass which contains the micro-organisms is frequently 



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