How did Leonard Landois explain black urine after transfusions between different animal species?

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Close-up illustration of multiple human red blood cells with their characteristic disc shape, floating against a red background. — blood group The major component of human blood is the red blood cell.

In 1875, the German physiologist Leonard Landois provided a scientific explanation for the appearance of black urine following the transfusion of heterologous blood (blood from a different species). He demonstrated that when red blood cells from one species are mixed with the serum of another, the cells typically clump together and may burst, a process known as hemolysis. Landois concluded that the black urine was a direct result of this hemolysis of incompatible red blood cells within the recipient's body.1