Analysis of information sources in references of the Wikipedia article "Bile" in English language version.
If blood is poured into a glass jar, a process of coagulation and sedimentation starts. It ends with four clearly distinct layers: a red region, a yellowish one, a black one, and a white one (Figure 4, left) ... The lowest part of the same column consists of sediment that is too dense to permit light to pass through. Therefore, this part of the column looks black and might be referred to as the 'black bile'. On the top of the column there is a white layer, which we today classify as fibrin; it might correspond to Galen's 'phlegm'. The remaining part is a rather clear but somewhat yellowish fluid that surrounds the coagulated column in the middle. It might be called 'yellow bile', but today we recognize it as blood serum.
