Under the names myohæmatin and histohæmatin MacMunn (1884-1886) described a respiratory pigment, which he found in muscles and other tissues of representatives of almost all the orders of the animal kingdom. He found that this pigment, in the reduced state, gives a characteristic spectrum, with four absorption bands occupying the following positions: 615—593/567·5—561/554·5—546/532—511/. When oxidized, the pigment does not show absorption bands. In 1887 MacMunn described a method by which it can be extracted in a “modified form” from the muscles of birds and mammals. He found the pectoral muscle of a pigeon to be the most suitable material for the extraction of “myohæmatin,” in the belief that it was the sole colouring matter of the muscles in a pigeon bled to death. From this “modified myohæmatin” he also obtained other derivatives, such as acid hæmatin and hæmatoporphyrin, and he finally arrived at the conclusion that myo- and histohæmatin are respiratory pigments different and independent from hæmoglobin and its derivatives. In 1889 Levy carefully repeated MacMunn’s experiments in extracting myohæmatin from muscles of birds and mammals and obtained the substance described by MacMunn as “modified myohæmatin. But he regarded this substance as an ordinary hæmochromogen, derived from hæmoglobin.