It is derived from the metabolism of salicin. The presence of salicin and salicylaldehyde can repel potential predators of leaf beetles. The active components include scopoletin, aesculetin, salicin, 1-methyl-2,3 clibutyl hemimellitate, and viburnin. Extended biochemical tests have characterized "P. penneri" as being uniformly salicin negative. Alder bark contains the anti-inflammatory salicin, which is metabolized into salicylic acid in the body. Salicylic acid, like aspirin, is a chemical derivative of salicin. The salicin in black haw may also be of use in pain relief. Both tannin and salicin can be extracted from goat willow bark. An example of an alcoholic glycoside is salicin, which is found in the genus "Salix". In 1829, salicin was used to develop aspirin. Populin, which occurs in the leaves and bark of "Populus tremula", is benzoyl salicin. Salicin was the historical origin of aspirin and is chemically related to it. Salix serpyllifolia contains salicin, the source of salicylic acid in aspirin. Salicin may cause an allergic skin reaction (skin sensitization; category 1). Like other willows, it contains salicin, and was used by Native Americans as a painkiller.