The site of healing over after a local injury in the heart.

The fluorochrome, Procion yellow, does not detectably penetrate the intact carciac cells of a living rat auricle, but stains the injured ifbers. When healing over is prevented in a calcium-free solution, the dye that penetrates through a point injury diffuses away from the damaged spot across the intercalated discs over a distance of several cell lengths. However, after an injury of the same size performed in a calcium-containing solution, Procion yellow is taken upt by one cardiac cell only or by a small integral number of cellular units to the exclusion of adjacent cells. It is concluded that the permeability of the discs of an injured cardiac cell decreases during healing over.