Crude drugs may be processed to separate crude fibre, which is a means of concentrating the more resistant cellular material of drugs for microscopic examination. This is especially applicable when the amount of foreign matter in a powder is small. Preparing a crude fibre concentrates the resistant parts of adulterants in a small amount of tissue thus facilitating better microscopic examination. It is particularly useful for starchy drugs such as ginger, which are rich in oleoresin and starch. The technique involves defatting the powder and boiling in turn with standard acid and alkali with suitable washing of the insoluble residue obtained in different stages. The procedure disintegrates the tissues readily such that the resistant material is suitable for microscopic study. The crude fibre so obtained is employed quantitatively to assay the fibre content of foods and animal feedstuff and also to detect crude drug adulteration, such as clove stalks in cloves. For detection of insect infestation, it is possible to further treat the crude fibre with acetic anhydride and sulphuric acid to destroy all lignified matter in the fibre. What is left will be only insect particles that may be easily visualized. Crude fibre values vary widely for many drugs making it difficult to apply as the only evidence of adulteration.