An experimental study of the effect of a wringer injury to the hind limbs of immature rats has been presented.

The findings in this study indicate that injuries produced by wringers extending over various periods of time (for example, sixty seconds versus 300 seconds) are similar histologically and vary only in degree. The histological preparations indicate that hemorrhage, edema, venous dilatation, leukocyte infiltration, and muscle necrosis may occur and that the injury is more severe near the bone. The changes first appear in from three to five hours and reach their maximum intensity in from sixteen to twenty-four hours. During this period the animals lose their ability to perform in a rat wheel.

Necrosis of striated muscle has been observed as well as late replacement of the necrotic muscle fibers by fibrous tissue. Regeneration of muscle fibers may occur after a wringer injury although the evidence in the present material is inadequate for this conclusion to be reached.

We have postulated that the factors giving rise to increased capillary pressure produce a condition of reduced oxygenation and ionic exchange at the fiber level and that these changes may produce muscle necrosis.