98 A MANUAL OF BACTERIOLOGY 



Scott 1 recommends the following as giving the most 

 perfect results with blood films, etc. : 



(1) Hold the freshly prepared and still wet film in the 

 mouth of a wide-mouthed bottle half filled with the 

 ordinary formalin solution, film side downwards, for five 

 seconds. 



(2) Drop, while still wet, film downwards, into absolute 

 alcohol. Leave for fifteen minutes, or, for convenience, 

 for any time up to forty- eight hours. 



The preparations may then be stained with methylene 

 blue, hsematoxylin and eosin, or with the Leishman or 

 Giemsa stain. (See also under " Malaria," Chapter XVIII.) 



Impression specimens. These are employed to examine 

 and preserve permanently the colonies or growths of 

 organisms so that their characteristic formation may be 

 observed. With plate cultivations this is very simple. 

 A clean cover-glass is sterilised in the flame and, having 

 cooled, is cautiously lowered on to a selected surface 

 colony with a sterile needle, avoiding all lateral movement. 

 It is then gently pressed on to the colony and then care- 

 fully raised by means of a couple of needles ; the colony 

 should adhere to the glass, and may be dried and fixed. 

 The colonies in gelatin tube cultures may also be used if 

 the gelatin is removed from the tube. This can be done 

 by dipping the tube for a few seconds into hot water ; 

 the gelatin round the walls of the tube will be melted, 

 and the gelatin mass can then be tilted out of the tube 

 on to a glass dish or tile. 



Stains and Staining Methods 



Micro-organisms being so minute and transparent, it 

 is usual to stain or dye them, so that they can be more 

 readily examined. In some instances organisms may have 



1 Journ. Path, and Bact., vol. vii, No. 1, p. 131. 



