The compensation of post-traumatic oedema in the rabbit at different ages.

1. The compensation of fluid loss from the circulation after an LD(50) period of bilateral hind-limb ischaemia in a thermoneutral environment has been studied in the rabbit from birth until young adulthood.2. The fluid loss from the circulation was calculated from the increase in the great vessel haematocrit value as the red cell volume and F(cells) were unchanged after limb ischaemia. This ;apparent' fluid loss was compared with the ;actual' fluid loss calculated from the increase in water content of the injured limbs.3. The 0- to 1-day-old rabbit was better able to restore fluid, and protein, to the circulation than the older animal and suffered a smaller percentage reduction in arterial blood pressure after an LD(50) period of ischaemia.4. The better compensation of post-traumatic fluid loss during the first 48 hr of life may be explained by the high capillary filtration coefficient and the post-traumatic increase in plasma protein osmotic pressure found at that age.5. The more efficient restoration of the plasma volume by the 0- to 1-day-old rabbit may account for the increased ability to withstand post-traumatic fluid loss at that age.