An article by J. Bartsch summarizing results from a German textile testing laboratory on how wool and cotton fibers are damaged. It describes microscopic and chemical methods, including pH measurement of acid concentration in paper-machine drying felts, and diazo and zinc-chloride-iodine staining tests. Twelve micrographs show scale damage, splits, brush ends, moth damage, and acid-parchmented and mercerized cotton fibers. It also covers acid damage to wool, hydrocellulose brittleness in cotton, and acid treatment of Swiss transparent cotton fabrics.