Analysis of fluid in capsules implanted into dog brain.

Perforated capsules were implanted aseptically into the brain parenchyma of dogs. The tissue and fluid formed within these intracerebral capsules (BC) were analysed for their ions and protein content. The results were compared with those for other perforated capsules implanted simultaneously into the subcutaneous tissue and muscle, respectively (denoted SC and MC). The following results were obtained: 1) In BC and MC, the Na/K ratio was different from that of the respective control tissues (cerebral parenchyma and temporal muscle) but similar to that of both the tissue in SC and control connective tissue. The water content of the three different capsular tissues was almost identical, but in each case different from that of the respective control tissues. 2) The Na/K ratio, Cl and protein content, and electrophoretic patterns of the three capsular fluids were similar to one another, and to serum. However, all (including BC fluid) were different in composition from the CSF (cerebrospinal fluid). 3) Investigations of the effect of time lapse after capsular implantation showed that the Na and K content was generally constant over the observed period, except that the K value was high in the initial few weeks. 4) Based on the results obtained, and on our data for pressure reequilibration in BC, the nature of the fluid compartment in BC is discussed. It is considered to represent an extension of the narrow space existing physiologically between the blood capillary wall and glial membrane, and not to be part of the true interstitial fluid compartment. 5) The barrier existing between the blood and brain parenchyma may be regarded not as a single membrane but as two membranes of dissimilar nature.