Prior to that it was assumed that the interstitial pressure Prior to that it was assumed that the interstitial pressure was positive, but with the use of this technique it was suggested that instead a negative pressure existed within the interstitial spaces. interstitial spaces. Other methods were developed later Other methods were developed later which confirm the capsular pressure registrations(15). which confirm the capsular pressure registrations (15). Among these the wick technique (28) offers an interesting, acute type of approach to interstitial dynamics. The wick acute type of approach to interstitial dynamics. The wick technique has, technique has, however, so far mainly been applied in however, so far mainly been applied in pressure measurements, while capsular fluid recently also has been quantitatively analyzed (5, 23). has been quantitatively analyzed (5, 23). The composition and function of the true interstitial The composition and function of the true interstitial fluid is, however, still a matter of dispute. In 1970 the more direct “liquid-parafhn cavity technique” for sampling of direct “liquid-parafhn cavity technique” for sampling of nanoliter quantities of interstitial fluid was introduced(17). nanoliter quantities of interstitial fluid was introduced (17). The electrolyte content of the fluid thus obtained was not in agreement with an ultrafiltrate of plasma and the here-in agreement with an ultrafiltrate of plasma and the here-upon expected Gibs-Donnan distribution across the capillary wall, although the protein content was in agreement with a hypothesized tissue fluid (19). Therefore, it was suggested that charged anionic macromolecules in the interstitial ground substance could affect the distribution of cations in the local tissue fluid. In situations in which there is disturbance of the normal tissue perfusion and hydration it has also been possible to show, with this direct technique, that significant compositional changes concerning electrolytes occur within the interstitium(16, 18); these results have later been reproduced by others adapting the same technique (8).

The present study deals with comparative analyses of the composition and dynamics of capsular fluid and tissue fluid obtained with the liquid-parafhn cavity technique. The objective is to determine which fluid, if any, that in reference to found parameters, most readily fulfills the concepts