Answer:
In acid-fast staining, carbon fuchsin is used as a primary stain which dissolves the mycolic acid present in the cell wall of <em>Mycobacterium smegmatis </em>and penetrates through it which results in staining <em>Mycobacterium</em> red.
Staphylococcus aureus cell wall does not contain mycolic acid so carbon fuchsin does not penetrate its cell wall, therefore, it becomes colorless after destaining with acid alcohol.
After destaining step methylene blue is added to stain non-acid-fast bacteria blue. So if I mistakenly forgot to use methylene blue during the procedure <em>Mycobacterium smegmatis</em> will appear red due to carbon fuchsin present in their cell wall and S<em>taphylococcus aureus</em> will appear colorless because it is destained.
Two pieces of cardboard one located at the bottom and one on top joint by card board with balls at the bottom and top all joint. hope you can picture that, it's rather confusing, sorry.
Hope this helps
