Light micrograph of a kidney showing several proximal convoluted tubules stained with the periodic acid Schiff (PAS) method. All are surrounded by a PAS positive basement membrane and have a brush border around the lumen, also positive with the PAS method. At this magnification the brush border seems formed by parallel filiform structures. They are the microvilli whose glycocalyx, rich in carbohydrates, is responsible for the positivity to PAS.