Abstract
The voluntary muscles of many animals, including birds, cats, and rabbits, can be clearly divided into two types, (a) red or dark, and (b) white or pale. In the first half of the Eighteenth' century it was generally assumed that the red color found in some muscles was brought about by increased blood supply to these muscles. It was not until 1865 that Kuhne (1) washed out the vascular systems of rabbits with saline, and than prepared extracts from the blood free muscles. Extracts from the pale muscles were colorless; those from the red muscles were a deep crimson. This shattered the theory that the coloration was due to increased blood supply and attention was turned to the possible relationship between contraction and pigmentation.