theory of two fluids

The two-fluids theory describes how blood flows through the heart, suggesting it contains two components: blood and a transparent, watery fluid called serum. According to this idea, blood is composed of these two "fluids" that mix but can be separated. This theory was an early attempt to understand blood circulation before the discovery of cells and molecules. It helped explain how blood moves and how different parts of blood serve different functions, but modern science now understands blood as a complex mix of cells, plasma, and other components rather than just two fluids.