Light micrograph of the substance inside a renal cyst. In this case, the cyst was part of a kidney with polycystic kidney disease, a type of genetic disorder where patients develop many cysts in their kidneys. The cyst contents are mostly made of protein and happened to form the interesting branching pattern photographed here. Haematoxylin and eosin stained tissue section. Magnification: 200x when printed at 10cm.