Microscopic examination of Mycobacteria. To demonstrate Leprosy bacilli (Mycobacterium leprae) causing leprosy, which are acid fast organisms. Mycobacterial cell walls contain a waxy substance composed of mycolic acids. The property of acid fastness is related to the carbon chain length of the mycolic acid found in any particular species (Lyon H 1991). The leprosy bacillus is much less acid and alcohol fast than the tubercle bacillus, therefore alcohol is removed from the hydrating and dehydrating steps. This technique combines peanut oil with the deparaffinizing solvent (xylene), minimizing the exposure of the bacteria's cell wall to organic solvents, thus protecting protect the more delicate waxy coat of the organisms.