Light micrograph of a kidney glomerulus stained with the periodic acid Schiff (PAS) method. The vascular tuft, located in the centre of the glomerulus, shows intense staining with PAS, which corresponds to the basement membranes of the glomerular capillaries. In many kidney diseases, the initial modifications consist of changes in this basement membrane of the glomerular capillaries, which can be detected using the PAS method.