King and Moore• suggested that there is an optimum specific gravity of approximately l •2 for the rate of passage of inert particles through the alimentary tract of the cow. Our results are similar, and show in addition that the time particles of equal weight are retained in the whole tract is a resultant of two complementary components each independently related to specific gravity.The relevance of this concept to the differential rates of passage of roughages and concentrate foods is being studied.One of us (M. F.) wishes to thank the University of Melbourne and the Australian Dairy Produce Board for financial help.

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The hand blood flows of Norwegian Lapps and North Norwegian fishermen were compared with those of a group of control subjects to determine whether habituation to cold alters the local vascular response. Blood flow was measured using venous occlusion plethysmographs with local temperatures of 40°, 20°, 10°C and a few degrees above zero. In further experiments using Dewar-flask calorimeters, the rate of heat elimination and rapidity of onset of the cold vasodilatation response on immersing the hand in water at 0°C were also recorded. The subjects were kept warm in order to remove as far as possible the effects of differing degrees of vasoconstrictor fiber activity. The onset of the cold vasodilatation was found to be more rapid in the cold-habituated subjects than in the control subjects. The levels of hand blood flow were, however, the same in all three groups of subjects, implying that habituation to cold does not alter the local vascular response to temperature. It is suggested that the difference reported by other workers in similar studies are probably found only when subjects examined are partially vasoconstricted, and reflect a more general process of adaptation to cold which results in a reduced vasoconstrictor fiber activity on exposure to a given thermal environment. Submitted on August 19, 1959

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