From the translation of a very old book...
To see why this is so it is necessary to appreciate the fact that meat is a muscle tissue, composed of muscle fibers, which is to say living, elongated cells with contractive properties. When the brain sends the signal, proteins within the fibers (mainly actin and myosin) slip past one another, shortening the muscle and causing it to contract. Additionally, the fibers are sheathed with a tough reinforcing tissue formed from a highly fibrous protein, collagen. The muscle tissue itself also contains fatty deposits and a circulatory system. The blood in this system conveys a number of different proteins, including small globular plasma proteins called serum albumin. There is therefore some albumin in meat, but very little.