CHAPTER IX. 



THE USE or STEONGEE STAINING SOLUTIONS. 



There are a large number of bacteria which do not 

 stain well, if only the simple aqueoas solutions of 

 aniline dyes are used. Either it takes an exceedingly 

 long time to produce at all a good result, or even after 

 several days the staining is incomplete. 



Amongst the species which occur in putrid meat, 

 etc., and of which we have made pure cultures, there 

 are very few which do not become stained with the 

 aqueous solutions. On the other hand, a number of 

 fluorescent bacilli, for example, only become very 

 badly coloured. Some of these are nearly always 

 present in impure water, and thus material for making 

 plate cultivations can be easily obtained from muddy 

 ditches, etc. 



Some of the colonies which develop in these culti- 

 vations are sure either to impart a greenish coloration 

 to the gelatine in their neighbourhood, or to render 

 it fluorescent. Generally several species of such 

 bacteria are present, and these we test with the stain- 

 ing solutions mentioned in Chapter VII., and select 



