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The alterations in contents of Na, K and water in thermally injuried explants of guinea-pig flank skin involve changes in both the cells and the interstitial material of the tissue. A full interpretation of the distribution of such changes can only be obtained if the volumes of cellular and extracellular fluid are known. This work examines the techniques of measuring extracellular fluid volume using 14C-inulin and 51Cr EDTA. Although it was found that the inulin preparation was excluded from a considerable part of the extracellular fluid of the skin explants, the space which it defined altered with increasing severity of thermal damage. The relationship of the inulin space with total water and with 51Cr EDTA space, which probably measures the total extracellular volume, provides an insight into the possible importance of changes in the nature of connective tissue in trauma. Alterations in fluid and cation balance between cells and their environment have been discussed in relation to increasing thermal damage. A clear sequence of events following the onset of the injury can be observed.

A number of changes in tissue content of Na, K and water are known to occur after injury. In order to elucidate the exact sequence of these changes, experiments were made on explants of guinea-pig flank skin maintained in vitro. This work explores some techniques using explants subjected to graded thermal injury (37 degrees-50 degrees). Stages of increasing damage were identified as higher temperatures were applied and these could be related to the developing changes in cation and water contents. This study is intended to explore a number of possible methods for use in a complete in vitro model to investigate particular problems and events associated with severe trauma.

1. Hydroxyethyl starch (HES) of molecular weight 450,000 has been extensively investigated as a plasma volume expander and HES of molecular weight 60,000 has been proposed for use as a cryoprotective agent in the freezing for preservation of red blood cells. In these applications considerable amounts of HES may be injected intravenously and it is therefore desirable to understand its behaviour in vivo.2. After intravenous injection into rabbits, plasma levels of HES and clinical dextrans were determined using anthrone. HES persisted longer in the circulation than did the dextrans.3. HES was recovered from the bloodstream of rabbits and shown by gel filtration to be of a narrower molecular size distribution than the injected material. Smaller molecules were removed, presumably by filtration at the glomerulus. Larger molecules may have been removed by cells of the reticuloendothelial system or possibly through the action of amylase.4. The amylase in saliva was shown to break down HES into molecules of intermediate size with very little production of maltose units.