THE STAINING OF BACTERIA IN SECTIONS 99 



by this process, which cannot be obtained by any other 

 method. 



The Staining of Bacteria in Sections. — There are a great 

 number of different methods published for the staining of 

 bacteria in sections of tissue. The following procedure is 

 common to most of the published methods : The sections 

 are transferred from the alcohol to water ; they are then 

 subjected to the action of the stain, which varies from a 

 few minutes to several hours. The time is in some cases 

 shortened by warming the staining solution. The sections 

 are washed, and then decolourised by some suitable 

 reagent ; the sections are again washed, then counter- 

 stained if necessary. The sections are now dehydrated with 

 alcohol, and then cleared with xylol or oil of cloves. 

 Xylol is preferable to oil of cloves as a clearing agent, as 

 it has no solvent action on the stains, does not resinify 

 on exposure, to the air, and evaporates without leaving a 

 deposit. Great care must be taken to remove all the water 

 from the section by means of alcohol before transferring to 

 the xylol, otherwise the section will not properly clear. 

 After remaining in the xylol for about five minutes, the 

 section is removed by means of a section-lifter, and then 

 laid out flat by careful manipulation with two small glass 

 rods on a clean microscope slip ; the excess of clearing 

 agent is removed by careful blotting with two or more 

 thicknesses of filter-paper. A drop of thick solution of 

 Canada balsam in xylol is dropped on the section, and a 

 cover-glass laid on in such a way that the drop of balsam 

 covers up the section, and extends over the whole under- 

 surface of the cover-glass, as in the case of simple cover- 

 glass preparations. The preparation is now ready for 

 examination with the oil immersion lens. 



Loffler's Method. — The sections are stained in Loffler's 

 methylene blue for from ten to twenty minutes. Super- 



