SUMMARY1. Investigations were made of the cation exchange capacity of fresh isolated ox corneal stroma (Q, units: mequiv fixed stromal charge/kg stromal fluid) at pH 7f4 over a variety of stomal hydrations (H, units: kg stromal fluid/kg dry tissue) both above and below the physiological hydration of 3-2, whilst the stromas were immersed in a variety of sodium chloride solutions (range 5-1000 mM).2. At any particular salt concentration, the product QH (dry tissue exchange capacity, units: mequiv/kg dry tissue) appeared constant, over all the hydrations investigated.3. Dry tissue exchange capacity (QH) varied, however, when the bathing salt concentration was altered. It varied between 55 mequiv/kg dry tissue (e.g. Q = 17 mequiv at H = 3-2) in 5 mM-NaCl to 240 mequiv/kg dry tissue (e.g. Q = 75 mequiv/l at H = 3'2) in 1000 mM-NaCl.4. The variation of stromal exchange capacity in NaCl solutions of different concentrations was similar when detected by three independent procedures: stromal gel pressure measurements, intrastromal sodium ion distributions, and intrastromal electrical potentials.5. Intrastromal chloride ion distributions were anomalous. Total chloride (measured by radio-isotopes) was consistently higher than that predicted by Donnan theory.6. The data were consistent with Elliott's hypothesis that a fraction of intrastromal chloride ions bind to the corneal stromal matrix and in so doing contribute to the fixed negative charge of the stroma.7. Our observations may be explained by a model of the cation exchange capacity of ox cornea which has two types of components. On is (at constant pH) invariant, and has a dry tissue exchange capacity of about 50 mequiv/kg dry tissue, and is probably generated by the sulphonic and carboxylic acid groups of the glycosaminoglyeans. The other is explained by supposing it to consist of a chloride binding ligand which exhibits first order binding, is half occupied at ambient chloride concentrations of 300 mm, and has a total capacity of 240 mequiv/kg dry tissue. 8. Partial stromal extraction with 4 M-guanidine HCl indicated that the chloride

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Dogs with simulated puncture wounds contaminated with reactor produced PuO, were studied to determine the relative translocation of Pu and Am. Differential distribution of the two elements was observed in both soft and skeletal tissues. Administration of the chelating agent diethylenetriaminepentaacetic acid, DTPA, produced significant effects in the relative concentration of Pu and Am in urine, liver, and femur bone tissues. In-viuo determination of Pu burdens by the ,**Am tracer method may produce inaccurate results.

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