Some observations of mycobacterial acid-fastness

Mycobacterial acid-fastness seems most readily explainable on the basis of a "lipids barrier principle" that in the first instance hinders penetration of the water-soluble dyestuff, and in the second, hinders penetration of the bleaching acid. Mycolic acids, and more especially, mycolate salts, in xylene solution complex and solubilize crystal violet, but the complex is demonstrably not stable even to weak acids. Stained mycobacterial preparations are readily bleached by an acidified lipid solvent; the destained preparations are nevertheless contribution to the barrier on which acid-fastness depends appears to reside in the mycoloyl-arabinogalactan of the cell wall.