Because natural cellulose is fundamentally fibrous, degradation—be it caused by chemical agents such as acids and alkalies, by physical agents such as grinding and ultrasonic vibration, or by biological agents such as molds and bacteria—proceeds in a manner which reflects this basic fibrillate structure. The dimensions of the threadlike fibrils into which cellulosebreaks down vary, dpedning upon the severity of the treatment and perhaps also on innate differences among celluloses from various sources. Following degradative action, light microscopy revealsfibrils of the order of several tenths of a micron in diameter. At the high magnifications obtainable with the electron microscope, still finer fibrils, a few hundred Angstroms wide, are detectable. Certain degradative treatments cause a further transverse splitting of these fibrils into rod-shaped structures. From x-ray and chemical investigations it is known that cellulose is made up of long-chain molecules whose arrangement with respect to one another gives rise to more or less ordered but poorly reactive crystalline regions and to disordered but easily reactive amorphous regions. Since microscopial studies show that many reactions proceed more easily in the regions between the fibrils than within the fibrils themselves, it appears that the crystalline cellulose is located principally in the fibrils, whereas the interfibrillar regions compose, in large measure, the amorphous fraction.