Complex sentence: In this period, he studied the chemical significance of the periodic acid-Schiff (PAS) staining method and showed that the method is not specific for carbohydrates as was thought at the time, but also stains lipids.
Split into simpler sentences: In this period, he studied the chemical significance of the periodic acid-Schiff (PAS) staining method. He showed that the method is not specific for carbohydrates as was thought at the time, but also stains lipids.