> The oily mixtures not only have a protective quality, they 
> also serve to
> "refatten" the deteriorated baccili, making them easier to 
> stain.  Please see
> Theory and practice of Histotechnology by Sheehan and 
> Hrapchak in the section
> on microorganisms.

Thanks a lot, You helped me a lot! For years I was wondering about that
reason.

Alex Nader