Salicin crystals. Polarized light micrograph of crystals of salicin marked with the letter 'X'. This sample is from a vintage prepared slide from the period 1870 - 1905. Salicin is an ingredient found in willow bark which may have anti-inflammatory activity. Historically, patients would chew on willow bark to relieve pain and inflammation. Salicin is converted to salicylic acid in the body and works in a similar way to aspirin. It may have limited use in treating pain and inflammation for example caused by some types of arthritis. Horizontal width of image is approximately 50 - 80 micrometres.