The roles of filtration and expression in the processing of digesta with high solid phase content.

The processes of filtration and expression of suspensions of biological solids are reviewed in the context of vertebrate digestion. We show that the digesta of the brushtail possum and sheep form a contiguous matrix of particles from which a fluid phase can be expressed by the application of pressure. These findings are examined in respect of their possible contribution to phase separation and the sorting of particles within the gastrointestinal tracts of vertebrates. The morphological adaptations and motility of various digestive compartments are related to the processing of digesta with high solid phase content, in particular the formation and dispersion of the particle matrices. A brief description is given of techniques for evaluating the properties of digesta with high solid phase content.