Liver of a DEN (Diethylnitrosamine)-treated rat. DEN is a toxic chemical which quickly induces liver cirrhosis followed by HCC (Hepatocellular carcinoma, a primary liver cancer). Cirrhosis is an end result of fibrosis, the scarring of liver tissue. Fibrosis is caused by the overproduction of collagen, a component of the connective tissue forming the liver. To grade the amount of cirrhosis present in a liver sample, collagen is made visible using the dye sirius red. Under polarized light, collagen is observed as the golden to red color as shown in this image.

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Credit: Liver of a DEN (Diethylnitrosamine)-treated rat. DEN is a toxic chemical which quickly induces liver cirrhosis followed by HCC (Hepatocellular carcinoma, a primary liver cancer). Cirrhosis is an end result of fibrosis, the scarring of liver tissue. Fibrosis is caused by the overproduction of collagen, a component of the connective tissue forming the liver. To grade the amount of cirrhosis present in a liver sample, collagen is made visible using the dye sirius red. Under polarized light, collagen is observed as the golden to red color as shown in this image. Tabea Hohensee. Source: Wellcome Collection.