PRACTICAL BACTERIOLOGY. 



The Staphylococcus pyogenes aureus, for example, 

 remains stained, when Gram's method is employed, 

 whilst the Micrococcus Gohorrlioeoe becomes de- 

 colourised. 



These methods of staining and decolourising are 

 especially useful for discovering bacteria in sections 

 of animal tissues. The sections are prepared in the 

 manner described in Chapter VIII. The best results 

 are certainly obtained by treating the section with 

 the aniline water staining solution rather than with 

 Ziehl's solution, or carbolic methylene blue. It is best 

 to use the solutions cold, because the elements of 

 animal tissues are less efiected by cold than by warm 

 solutions, whilst the bacteria are sure to absorb suflS- 

 cient colouring matter if they are left in long enough. 

 After the staining is completed, decolouriaation may 

 be effected either by Gram's method, or by means of 

 -Q per cent, nitric acid ; the sections must then 

 be rinsed in absolute alcohol, in order to remove all 

 the rest of the acid and the colouring matter. If it is 

 wished to examine them at once, it is best to place 

 each section in a drop of water upon a slide, and to 

 cover it with a cover-glass. If they are to bo kept, 

 they must be treated in the manner described in 

 Chapter XII. 



The method of staining the sections must depend 

 upon the kind of organisms which we expect to find. 

 The special treatment necessary for pathogenic 



