Regeneration fo the completely excised gastrocnemius muscle in the frog and rat from minced muscle fragments.

In 85 frogs and 29 rats, the entire gastrocnemius muscle was removed. After removal of as much connective tissue as possible, about two-thirds of the remaining muscle was finely minced with a scissors. These minced fragments were orthotopically re-implanted, and the overlying skin was sutured. As the implanted muscle fragments degenerate, new muscle fibers appears in the regenerate. The proportion of connective tissue to muscle is usually greater than normal, especially in the frog. Grossly, normal relationships are established with the cut ends of the Achilles and proximal tendons, as well as with the blood vessels and nerves. The total diameter of the regenerated muscle is almost always less than half of that seen in normal muscles. Regeneration of muscle is much more extensive in the rat than in the frog, and it occurs almost twice as rapidly. The histology of the regenerative process is described for both the frog and the rat. Regeneration is a term which encompasses a number of distinctly different processes leading to the restoration of a missing part or to the duplication of a structure which is already present. The extent of regeneration may range from the restoration of an entire limb to the healing of relatively small defects in individual tissues or organs. Limb regeneration is considered to be an epimorphic process, occurring in a morphogenetic field and guided and controlled by a complex series of events involving the cooperation of nerves, the apical epidermis and other less well studied factors. In vertebrates the capacity for limb regeneration is highest in urodele amphibians and in premetamorphic anurans, but limb regeneration occurs sporadically and abortively in adult anurans and certain lizards. In higher vertebrates there has been little published evidence of limb regeneration. A certain degree of restoration of limb regeneration has been induced in adult anura by experimental means such as severe mechanical trauma (Polezhaev, '46), chemical irritation (Rose, '45), supplemental innervation (Singer, '54) and implantation of additional adrenal tissue (Schotte and Wilbur, '58). Regeneration of tissue defects has been studied more extensively in higher verteJ. MORPH., 125: 447-472. brates, and in almost all cases individual tissues have been shown to have the capacity to repair small defects (McMinn,