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1. It was shown that when polyethylene glycol (PEG) was added to suspensions of food particles in aqueous buffer solutions, its distribution in the total water of the food mass was not uniform. The marker was excluded from a large proportion of the water contained in the swollen food particles. This effect was independent of temperature, pH, and, within limits, the time of contact.
2. It was shown that the theoretical concentration (C0), assuming a uniform distribution of marker, could be calculated from the observed concentration (C), weight of food in suspension (W) and the total volume of water (V), using the equation C = C0(I + b[W/V]) where b is constant for any given food. The addition of PEG solution to dry food particles gave a smaller effect.
3. The distribution of PEG was usually, but not invariably, more uniform in a suspension of roughages than in a suspension of concentrates.
4. Possible implications of these findings with respect to marker experiments with PEG are discussed.